diff --git a/internal/client/client.go b/internal/client/client.go
index afefce1..6f331f3 100644
--- a/internal/client/client.go
+++ b/internal/client/client.go
@@ -69,6 +69,8 @@ func Run(ctx context.Context, options Options) (probe.Summary, error) {
 	if err != nil {
 		return probe.Summary{}, err
 	}
+	var samples []probe.Sample
+	var startedAt time.Time
 	complete := false
 	defer func() {
 		if !complete {
@@ -77,12 +79,24 @@ func Run(ctx context.Context, options Options) (probe.Summary, error) {
 			_ = cancelSession(cancelCtx, &httpClient, server, session.CancelURL)
 		}
 	}()
+	completePartial := func(original error) (probe.Summary, error) {
+		if len(samples) == 0 || startedAt.IsZero() {
+			return probe.Summary{}, original
+		}
+		finishedAt := time.Now().UTC()
+		completeCtx, cancel := context.WithTimeout(context.Background(), cancelRequestTimeout(options.Timeout))
+		defer cancel()
+		if _, completeErr := completeSession(completeCtx, &httpClient, server, session.CompleteURL, startedAt, finishedAt, samples); completeErr != nil {
+			return probe.Summary{}, fmt.Errorf("%w; also failed to complete partial test session: %v", original, completeErr)
+		}
+		complete = true
+		return probe.Summary{}, original
+	}
 
 	if err := waitForQueue(ctx, &httpClient, server, session, options); err != nil {
 		return probe.Summary{}, err
 	}
 
-	var samples []probe.Sample
 	record := func(sample probe.Sample) {
 		samples = append(samples, sample)
 		if options.OnSample != nil {
@@ -90,18 +104,18 @@ func Run(ctx context.Context, options Options) (probe.Summary, error) {
 		}
 	}
 
-	startedAt := time.Now().UTC()
+	startedAt = time.Now().UTC()
 	record(measureLatency(ctx, &httpClient, server))
 	if err := runPhase(ctx, options.Duration, func() probe.Sample {
 		return measureDownload(ctx, &httpClient, server, session.DownloadURL, options.DownloadBytes)
 	}, record); err != nil {
-		return probe.Summary{}, err
+		return completePartial(err)
 	}
 	record(measureLatency(ctx, &httpClient, server))
 	if err := runPhase(ctx, options.Duration, func() probe.Sample {
 		return measureUpload(ctx, &httpClient, server, session.UploadURL, options.UploadBytes)
 	}, record); err != nil {
-		return probe.Summary{}, err
+		return completePartial(err)
 	}
 	record(measureLatency(ctx, &httpClient, server))
 	finishedAt := time.Now().UTC()
diff --git a/internal/client/client_test.go b/internal/client/client_test.go
index 1a0c1fa..cabace3 100644
--- a/internal/client/client_test.go
+++ b/internal/client/client_test.go
@@ -131,6 +131,44 @@ func TestRunCancelsQueuedSessionWhenContextStops(t *testing.T) {
 	}
 }
 
+func TestRunPersistsPartialRecordWhenCanceledAfterSamples(t *testing.T) {
+	store := &memoryStore{}
+	server := appweb.New(appweb.Options{Store: store, Runner: noopRunner})
+	httpServer := httptest.NewServer(server.Handler())
+	defer httpServer.Close()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	canceled := false
+	_, err := Run(ctx, Options{
+		ServerURL:     httpServer.URL,
+		Duration:      time.Second,
+		Timeout:       time.Second,
+		DownloadBytes: 1024,
+		UploadBytes:   512,
+		OnSample: func(sample probe.Sample) {
+			if sample.Kind == "download" && !canceled {
+				canceled = true
+				cancel()
+			}
+		},
+	})
+	if !errors.Is(err, context.Canceled) {
+		t.Fatalf("Run error = %v, want context canceled", err)
+	}
+
+	records := store.snapshot()
+	if len(records) != 1 {
+		t.Fatalf("records = %d, want one partial record", len(records))
+	}
+	if !hasKind(records[0].Samples, "download") {
+		t.Fatalf("samples = %#v, want partial download sample persisted", records[0].Samples)
+	}
+	if records[0].Summary.Samples != len(records[0].Samples) {
+		t.Fatalf("summary samples = %d, want %d", records[0].Summary.Samples, len(records[0].Samples))
+	}
+}
+
 func TestRunIperf3CompletesOneOffServerSession(t *testing.T) {
 	store := &memoryStore{}
 	server := appweb.New(appweb.Options{Store: store, Runner: noopRunner, Iperf3Path: fakeIperf3(t)})
diff --git a/web/assets_test.go b/web/assets_test.go
index 24d85bc..a21037d 100644
--- a/web/assets_test.go
+++ b/web/assets_test.go
@@ -104,6 +104,19 @@ func TestStaticAssetsIncludeManualCancelBehavior(t *testing.T) {
 	}
 }
 
+func TestStaticAssetsPersistPartialBrowserStop(t *testing.T) {
+	app, err := readAsset("app.js")
+	if err != nil {
+		t.Fatalf("read app.js: %v", err)
+	}
+	if !contains(app, "completeCurrentSession") ||
+		!contains(app, "session.completeUrl") ||
+		!contains(app, "state.samples.length") ||
+		!contains(app, "已保存已完成样本") {
+		t.Fatalf("app.js missing partial browser stop persistence behavior")
+	}
+}
+
 func TestStaticAssetsLabelTransferSamplesAsInstantaneous(t *testing.T) {
 	app, err := readAsset("app.js")
 	if err != nil {
diff --git a/web/static/app.js b/web/static/app.js
index 892856e..090b660 100644
--- a/web/static/app.js
+++ b/web/static/app.js
@@ -6,6 +6,8 @@ const state = {
   currentSession: null,
   abortController: null,
   cancelRequested: false,
+  startedAt: null,
+  partialSaved: false,
 };
 
 const els = {
@@ -46,7 +48,9 @@ window.addEventListener("resize", () => {
 });
 window.addEventListener("beforeunload", () => {
   state.cancelRequested = true;
-  cancelCurrentSession({ beacon: true });
+  if (!completeCurrentSession({ beacon: true, partial: true })) {
+    cancelCurrentSession({ beacon: true });
+  }
 });
 
 initializeDefaultTarget();
@@ -106,10 +110,13 @@ async function stopCurrentTest() {
   if (state.abortController) {
     state.abortController.abort();
   }
-  await cancelCurrentSession();
+  const saved = await completeCurrentSession({ partial: true });
+  if (!saved) {
+    await cancelCurrentSession();
+  }
   closeSource();
   setServerState("idle", "空闲");
-  setNotice("测试已停止，队列已释放。");
+  setNotice(saved ? "测试已停止，已保存已完成样本。" : "测试已停止，队列已释放。");
   setTestingControls(false);
 }
 
@@ -135,6 +142,56 @@ async function cancelCurrentSession(options = {}) {
   }
 }
 
+function completeCurrentSession(options = {}) {
+  const session = state.currentSession;
+  if (!session || !session.completeUrl || !state.samples.length) {
+    return false;
+  }
+  const startedAt = state.startedAt || new Date();
+  const body = JSON.stringify({
+    startedAt: startedAt.toISOString(),
+    finishedAt: new Date().toISOString(),
+    samples: state.samples,
+  });
+
+  if (options.beacon && navigator.sendBeacon) {
+    const sent = navigator.sendBeacon(session.completeUrl, new Blob([body], { type: "application/json" }));
+    if (sent) {
+      state.currentSession = null;
+      state.partialSaved = Boolean(options.partial);
+    }
+    return sent;
+  }
+
+  return completeCurrentSessionWithFetch(session, body, options);
+}
+
+async function completeCurrentSessionWithFetch(session, body, options = {}) {
+  try {
+    const fetchOptions = {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body,
+      cache: "no-store",
+    };
+    if (options.keepalive) {
+      fetchOptions.keepalive = true;
+    }
+    const response = await fetch(session.completeUrl, fetchOptions);
+    const payload = await response.json();
+    if (!response.ok) {
+      throw new Error(payload.error || "保存测试记录失败");
+    }
+    state.currentSession = null;
+    state.partialSaved = Boolean(options.partial);
+    updateSummary(payload.summary);
+    await loadRecords();
+    return true;
+  } catch (error) {
+    return false;
+  }
+}
+
 async function startTest(event) {
   event.preventDefault();
   closeSource();
@@ -142,6 +199,8 @@ async function startTest(event) {
   state.currentSession = null;
   state.cancelRequested = false;
   state.abortController = new AbortController();
+  state.startedAt = null;
+  state.partialSaved = false;
   els.eventLog.textContent = "";
   setNotice("");
   setServerState("running", "运行中");
@@ -183,7 +242,7 @@ async function startTest(event) {
     }
     if (state.cancelRequested || error.name === "AbortError") {
       setServerState("idle", "空闲");
-      setNotice("测试已停止，队列已释放。");
+      setNotice(state.partialSaved ? "测试已停止，已保存已完成样本。" : "测试已停止，队列已释放。");
     } else {
       setServerState("error", "错误");
       setNotice(error.message, true);
@@ -191,6 +250,8 @@ async function startTest(event) {
   } finally {
     state.abortController = null;
     state.currentSession = null;
+    state.startedAt = null;
+    state.partialSaved = false;
     setTestingControls(false);
   }
 }
@@ -227,7 +288,7 @@ async function waitForBrowserQueue(session) {
 }
 
 async function runBrowserSpeedTest(session, request) {
-  const startedAt = new Date();
+  state.startedAt = new Date();
   const durationMs = Math.max(1000, (request.durationSeconds || 30) * 1000);
 
   throwIfCanceled();
@@ -242,27 +303,11 @@ async function runBrowserSpeedTest(session, request) {
   await measureLatency(request.timeoutMillis);
   throwIfCanceled();
 
-  const finishedAt = new Date();
-  const response = await fetch(session.completeUrl, {
-    method: "POST",
-    headers: { "Content-Type": "application/json" },
-    body: JSON.stringify({
-      startedAt: startedAt.toISOString(),
-      finishedAt: finishedAt.toISOString(),
-      samples: state.samples,
-    }),
-    signal: state.abortController && state.abortController.signal,
-  });
-  const body = await response.json();
-  if (!response.ok) {
-    throw new Error(body.error || "保存测试记录失败");
+  if (!await completeCurrentSession()) {
+    throw new Error("保存测试记录失败");
   }
-
-  updateSummary(body.summary);
-  state.currentSession = null;
   setServerState("idle", "空闲");
   setNotice("浏览器上传/下载测速完成，记录已保存。");
-  await loadRecords();
 }
 
 async function runTransferPhase(durationMs, measure) {