diff --git a/frontend/src/components/network-quality-indicator.tsx b/frontend/src/components/network-quality-indicator.tsx
new file mode 100644
index 0000000..05e4343
--- /dev/null
+++ b/frontend/src/components/network-quality-indicator.tsx
@@ -0,0 +1,70 @@
+"use client";
+
+import { Wifi, WifiOff } from "lucide-react";
+
+import type {
+  NetworkQuality,
+  VoicePreviewStatus,
+} from "@/hooks/use-voice-preview";
+
+const QUALITY_VIEW: Record<
+  NetworkQuality,
+  { label: string; color: string; darkColor: string }
+> = {
+  unknown: {
+    label: "检测中",
+    color: "text-muted-foreground",
+    darkColor: "text-white/55",
+  },
+  good: {
+    label: "网络良好",
+    color: "text-emerald-600",
+    darkColor: "text-emerald-300",
+  },
+  fair: {
+    label: "网络一般",
+    color: "text-amber-600",
+    darkColor: "text-amber-300",
+  },
+  poor: {
+    label: "网络较差",
+    color: "text-red-600",
+    darkColor: "text-red-300",
+  },
+};
+
+export function NetworkQualityIndicator({
+  quality,
+  status,
+  dark = false,
+  className = "",
+}: {
+  quality: NetworkQuality;
+  status: VoicePreviewStatus;
+  dark?: boolean;
+  className?: string;
+}) {
+  const connected = status === "connected";
+  const qualityView = QUALITY_VIEW[quality];
+  const view = connected
+    ? {
+        label: qualityView.label,
+        color: dark ? qualityView.darkColor : qualityView.color,
+      }
+    : {
+        label: status === "connecting" ? "检测中" : "未连接",
+        color: dark ? "text-white/55" : "text-muted-foreground",
+      };
+  const Icon = connected || status === "connecting" ? Wifi : WifiOff;
+
+  return (
+    <span
+      className={`inline-flex items-center gap-1.5 whitespace-nowrap text-xs ${view.color} ${className}`}
+      title={view.label}
+      aria-label={view.label}
+    >
+      <Icon className="size-3.5" aria-hidden="true" />
+      <span>{view.label}</span>
+    </span>
+  );
+}
diff --git a/frontend/src/components/pages/AssistantPage.tsx b/frontend/src/components/pages/AssistantPage.tsx
index 5d632cc..9e21b56 100644
--- a/frontend/src/components/pages/AssistantPage.tsx
+++ b/frontend/src/components/pages/AssistantPage.tsx
@@ -40,6 +40,7 @@ import {
 
 import { Button } from "@/components/ui/button";
 import { Badge } from "@/components/ui/badge";
+import { NetworkQualityIndicator } from "@/components/network-quality-indicator";
 import { Input } from "@/components/ui/input";
 import { Textarea } from "@/components/ui/textarea";
 import { Switch } from "@/components/ui/switch";
@@ -2037,6 +2038,10 @@ function DebugDrawer({
           <div className="shrink-0 text-sm font-medium text-foreground">
             调试与预览
           </div>
+          <NetworkQualityIndicator
+            quality={preview.networkQuality}
+            status={preview.status}
+          />
           <DebugConnectionStatus
             status={preview.status}
             micWarning={preview.micWarning}
diff --git a/frontend/src/components/pages/MobileCallPage.tsx b/frontend/src/components/pages/MobileCallPage.tsx
index 1ddd137..e766c3e 100644
--- a/frontend/src/components/pages/MobileCallPage.tsx
+++ b/frontend/src/components/pages/MobileCallPage.tsx
@@ -12,6 +12,7 @@ import {
   Video,
 } from "lucide-react";
 import { Button } from "@/components/ui/button";
+import { NetworkQualityIndicator } from "@/components/network-quality-indicator";
 import {
   DropdownMenu,
   DropdownMenuContent,
@@ -247,6 +248,7 @@ export function MobileCallPage({ assistantId }: { assistantId: string }) {
     selectOutputDevice,
     supportsOutputSelection,
     messages,
+    networkQuality,
     connect,
     replaceVideoStream,
     disconnect,
@@ -325,6 +327,13 @@ export function MobileCallPage({ assistantId }: { assistantId: string }) {
 
       {view === "chat" && <MobileCallTranscript messages={messages} />}
 
+      <NetworkQualityIndicator
+        quality={networkQuality}
+        status={status}
+        dark
+        className="absolute left-4 top-[max(1rem,env(safe-area-inset-top))] z-10 rounded-full border border-white/10 bg-black/30 px-3 py-1.5 backdrop-blur-md"
+      />
+
       <div className="absolute left-1/2 top-[max(1rem,env(safe-area-inset-top))] z-10 flex -translate-x-1/2 items-center gap-2 rounded-full border border-white/10 bg-black/30 px-3 py-1.5 text-xs text-white/85 backdrop-blur-md">
         <span
           className={[
diff --git a/frontend/src/hooks/use-camera-preview.ts b/frontend/src/hooks/use-camera-preview.ts
index d5cc5d7..c1a39ea 100644
--- a/frontend/src/hooks/use-camera-preview.ts
+++ b/frontend/src/hooks/use-camera-preview.ts
@@ -9,6 +9,12 @@
 
 import { useCallback, useEffect, useRef, useState } from "react";
 
+const CAMERA_VIDEO_CONSTRAINTS: MediaTrackConstraints = {
+  width: { ideal: 640, max: 640 },
+  height: { ideal: 360, max: 480 },
+  frameRate: { ideal: 12, max: 15 },
+};
+
 function cameraErrorMessage(error: unknown): string {
   if (error instanceof DOMException) {
     if (error.name === "NotAllowedError")
@@ -59,8 +65,12 @@ export function useCameraPreview() {
     setStarting(true);
     try {
       const id = deviceIdRef.current;
+      const videoConstraints: MediaTrackConstraints = {
+        ...CAMERA_VIDEO_CONSTRAINTS,
+        ...(id ? { deviceId: { exact: id } } : {}),
+      };
       const media = await navigator.mediaDevices.getUserMedia({
-        video: id ? { deviceId: { exact: id } } : true,
+        video: videoConstraints,
       });
       streamRef.current = media;
       setStream(media);
diff --git a/frontend/src/hooks/use-voice-preview.ts b/frontend/src/hooks/use-voice-preview.ts
index 2be42f9..7f46bde 100644
--- a/frontend/src/hooks/use-voice-preview.ts
+++ b/frontend/src/hooks/use-voice-preview.ts
@@ -22,6 +22,30 @@ import { useCallback, useEffect, useRef, useState } from "react";
 import { API_BASE, webrtcApi } from "@/lib/api";
 
 export type VoicePreviewStatus = "idle" | "connecting" | "connected" | "failed";
+export type NetworkQuality = "unknown" | "good" | "fair" | "poor";
+
+const NETWORK_SAMPLE_INTERVAL_MS = 2_000;
+const VIDEO_BITRATE_BY_QUALITY: Record<
+  Exclude<NetworkQuality, "unknown">,
+  number
+> = {
+  good: 600_000,
+  fair: 500_000,
+  poor: 300_000,
+};
+const INITIAL_VIDEO_BITRATE = VIDEO_BITRATE_BY_QUALITY.fair;
+
+type NetworkStatsSample = {
+  packetsSent: number;
+  packetsLost: number;
+};
+
+type VideoNetworkMetrics = {
+  packetsSent: number | null;
+  packetsLost: number | null;
+  roundTripTime: number | null;
+  availableOutgoingBitrate: number | null;
+};
 
 type ConnectOptions = {
   visionEnabled?: boolean;
@@ -88,6 +112,97 @@ function microphoneErrorMessage(error: unknown): string {
   return errorMessage(error, "无法访问麦克风。");
 }
 
+async function setVideoBitrate(
+  sender: RTCRtpSender,
+  bitrate: number,
+): Promise<boolean> {
+  try {
+    const parameters = sender.getParameters();
+    if (!parameters.encodings.length) parameters.encodings = [{}];
+    parameters.encodings[0].maxBitrate = bitrate;
+    parameters.degradationPreference = "maintain-resolution";
+    await sender.setParameters(parameters);
+    return true;
+  } catch {
+    // 不支持发送参数的浏览器继续使用 WebRTC 自带的拥塞控制。
+    return false;
+  }
+}
+
+function readVideoNetworkMetrics(report: RTCStatsReport): VideoNetworkMetrics {
+  const metrics: VideoNetworkMetrics = {
+    packetsSent: null,
+    packetsLost: null,
+    roundTripTime: null,
+    availableOutgoingBitrate: null,
+  };
+
+  report.forEach((stat) => {
+    const values = stat as RTCStats & Record<string, unknown>;
+    const kind = values.kind ?? values.mediaType;
+    if (values.type === "outbound-rtp" && kind === "video") {
+      if (typeof values.packetsSent === "number") {
+        metrics.packetsSent = values.packetsSent;
+      }
+    } else if (values.type === "remote-inbound-rtp" && kind === "video") {
+      if (typeof values.packetsLost === "number") {
+        metrics.packetsLost = values.packetsLost;
+      }
+      if (typeof values.roundTripTime === "number") {
+        metrics.roundTripTime = values.roundTripTime;
+      }
+    } else if (
+      values.type === "candidate-pair" &&
+      values.state === "succeeded" &&
+      (values.nominated === true || values.selected === true)
+    ) {
+      if (typeof values.currentRoundTripTime === "number") {
+        metrics.roundTripTime = values.currentRoundTripTime;
+      }
+      if (typeof values.availableOutgoingBitrate === "number") {
+        metrics.availableOutgoingBitrate = values.availableOutgoingBitrate;
+      }
+    }
+  });
+
+  return metrics;
+}
+
+function classifyNetworkQuality(
+  metrics: VideoNetworkMetrics,
+  previous: NetworkStatsSample | null,
+): NetworkQuality {
+  const hasPacketSample =
+    previous !== null &&
+    metrics.packetsSent !== null &&
+    metrics.packetsLost !== null;
+  const sentDelta = hasPacketSample
+    ? Math.max(0, metrics.packetsSent! - previous.packetsSent)
+    : 0;
+  const lostDelta = hasPacketSample
+    ? Math.max(0, metrics.packetsLost! - previous.packetsLost)
+    : 0;
+  const lossRate = sentDelta > 0 ? lostDelta / sentDelta : null;
+  const { roundTripTime: rtt, availableOutgoingBitrate: bandwidth } = metrics;
+
+  if (lossRate === null && rtt === null && bandwidth === null) return "unknown";
+  if (
+    (lossRate !== null && lossRate >= 0.08) ||
+    (rtt !== null && rtt >= 0.45) ||
+    (bandwidth !== null && bandwidth < 350_000)
+  ) {
+    return "poor";
+  }
+  if (
+    (lossRate !== null && lossRate >= 0.03) ||
+    (rtt !== null && rtt >= 0.25) ||
+    (bandwidth !== null && bandwidth < 550_000)
+  ) {
+    return "fair";
+  }
+  return "good";
+}
+
 export function useVoicePreview(
   assistantId: string | null,
   onNodeActive?: (nodeId: string | null) => void,
@@ -99,6 +214,8 @@ export function useVoicePreview(
   // 远端(助手 TTS)媒体流:除挂到 <audio> 播放外,也暴露给波形可视化
   const [remoteStream, setRemoteStream] = useState<MediaStream | null>(null);
   const [messages, setMessages] = useState<ChatMessage[]>([]);
+  const [networkQuality, setNetworkQuality] =
+    useState<NetworkQuality>("unknown");
   // 可选麦克风/扬声器列表与当前选择(空串表示交给浏览器选默认设备)
   const [audioInputs, setAudioInputs] = useState<MediaDeviceInfo[]>([]);
   const [audioOutputs, setAudioOutputs] = useState<MediaDeviceInfo[]>([]);
@@ -114,6 +231,8 @@ export function useVoicePreview(
   const localStreamRef = useRef<MediaStream | null>(null);
   const startingRef = useRef(false);
   const messageSeqRef = useRef(0);
+  const networkStatsRef = useRef<NetworkStatsSample | null>(null);
+  const videoBitrateRef = useRef(INITIAL_VIDEO_BITRATE);
   // 后端主动结束(工作流走到结束节点)标记:据此把随后的断开当作正常结束而非报错
   const endedByServerRef = useRef(false);
   // 工作流激活节点回调存进 ref,避免把它挂进 connect 依赖反复重建连接
@@ -233,6 +352,9 @@ export function useVoicePreview(
     messageSeqRef.current = 0;
     setError(null);
     setMicWarning(null);
+    setNetworkQuality("unknown");
+    networkStatsRef.current = null;
+    videoBitrateRef.current = INITIAL_VIDEO_BITRATE;
     setStatus("idle");
   }, [releaseResources]);
 
@@ -242,6 +364,9 @@ export function useVoicePreview(
       setLocalStream(null);
       setRemoteStream(null);
       setError(message);
+      setNetworkQuality("unknown");
+      networkStatsRef.current = null;
+      videoBitrateRef.current = INITIAL_VIDEO_BITRATE;
       setStatus("failed");
     },
     [releaseResources],
@@ -500,9 +625,10 @@ export function useVoicePreview(
         pc.addTransceiver("audio", { direction: "recvonly" });
       }
       if (options.videoStream) {
-        options.videoStream
-          .getVideoTracks()
-          .forEach((track) => pc.addTrack(track, options.videoStream!));
+        for (const track of options.videoStream.getVideoTracks()) {
+          const sender = pc.addTrack(track, options.videoStream);
+          await setVideoBitrate(sender, INITIAL_VIDEO_BITRATE);
+        }
       }
 
       // 4) 生成 offer 并发给后端(assistant_id 在 payload 顶层)
@@ -531,6 +657,51 @@ export function useVoicePreview(
     }
   }, [assistantId, applyOutputDevice, fail, closeOnRemoteEnd, refreshDevices]);
 
+  useEffect(() => {
+    if (status !== "connected") return;
+    const pc = pcRef.current;
+    if (!pc) return;
+
+    let cancelled = false;
+    const sampleNetwork = async () => {
+      try {
+        const metrics = readVideoNetworkMetrics(await pc.getStats());
+        if (cancelled || pcRef.current !== pc) return;
+        const quality = classifyNetworkQuality(metrics, networkStatsRef.current);
+        if (metrics.packetsSent !== null && metrics.packetsLost !== null) {
+          networkStatsRef.current = {
+            packetsSent: metrics.packetsSent,
+            packetsLost: metrics.packetsLost,
+          };
+        }
+        setNetworkQuality(quality);
+
+        if (quality === "unknown") return;
+        const bitrate = VIDEO_BITRATE_BY_QUALITY[quality];
+        if (bitrate === videoBitrateRef.current) return;
+        const sender = pc
+          .getSenders()
+          .find((item) => item.track?.kind === "video");
+        if (!sender) return;
+        if (await setVideoBitrate(sender, bitrate)) {
+          videoBitrateRef.current = bitrate;
+        }
+      } catch {
+        // 个别浏览器不提供完整 WebRTC 统计信息时，保留底层拥塞控制。
+      }
+    };
+
+    void sampleNetwork();
+    const interval = window.setInterval(
+      () => void sampleNetwork(),
+      NETWORK_SAMPLE_INTERVAL_MS,
+    );
+    return () => {
+      cancelled = true;
+      window.clearInterval(interval);
+    };
+  }, [status]);
+
   const replaceVideoStream = useCallback(
     async (videoStream: MediaStream | null) => {
       const pc = pcRef.current;
@@ -621,6 +792,7 @@ export function useVoicePreview(
     localStream,
     remoteStream,
     messages,
+    networkQuality,
     audioInputs,
     audioOutputs,
     selectedDeviceId,