diff --git a/backend/app/adapters/device_client.py b/backend/app/adapters/device_client.py
index 15ac20c..4c2ae90 100644
--- a/backend/app/adapters/device_client.py
+++ b/backend/app/adapters/device_client.py
@@ -446,7 +446,7 @@ class MockDeviceClient(DeviceClient):
         return dict(self._system_config)
 
     def read_time_sync_config(self) -> Dict[str, str]:
-        return {"time_sync": str(self._system_config.get("time_sync", ""))}
+        return {"time_sync": datetime.now().strftime("%Y-%m-%d %H:%M:%S")}
 
     def read_net_config(self, nic: str) -> Dict[str, Any]:
         for item in self._net_config:
diff --git a/backend/tests/test_api.py b/backend/tests/test_api.py
index aeb5158..cd8a18b 100644
--- a/backend/tests/test_api.py
+++ b/backend/tests/test_api.py
@@ -1,4 +1,5 @@
-from datetime import datetime
+import asyncio
+from datetime import datetime, timedelta
 
 from fastapi.testclient import TestClient
 
@@ -11,11 +12,17 @@ from app.repositories.alarm_repo import AlarmRepository
 from app.repositories.json_config_repo import JsonConfigRepository
 from app.schemas.platform import AlarmEvent, LineData, RealtimeData, ValueGroup
 from app.services.platform_service import platform_service
+from app.ws.manager import ws_manager
 
 
 client = TestClient(app)
 
 
+def _assert_time_sync_in_window(value: str, before: datetime, after: datetime) -> None:
+    parsed = datetime.strptime(value, "%Y-%m-%d %H:%M:%S")
+    assert before - timedelta(seconds=1) <= parsed <= after + timedelta(seconds=1)
+
+
 def test_healthcheck() -> None:
     response = client.get("/")
     assert response.status_code == 200
@@ -169,7 +176,9 @@ def test_config_query_endpoints(tmp_path) -> None:
         line_alarm_response = client.get("/api/config/line_alarm_setting", headers=headers, params={"line_no": 1})
         ai_alarm_response = client.get("/api/config/ai_alarm_setting", headers=headers)
         system_response = client.get("/api/config/system", headers=headers)
+        before_time_sync = datetime.now()
         time_sync_response = client.get("/api/config/time-sync", headers=headers)
+        after_time_sync = datetime.now()
 
         assert device_response.status_code == 200
         assert net_response.status_code == 200
@@ -190,7 +199,7 @@ def test_config_query_endpoints(tmp_path) -> None:
         assert line_alarm_response.json()["data"]["transformer_change"][0]["category"] == "PT变化"
         assert ai_alarm_response.json()["data"][0]["channel_no"] == 1
         assert system_response.json()["data"]["time_sync"] == "2026-05-25 12:34:56"
-        assert time_sync_response.json()["data"]["time_sync"] == "2026-05-25 12:34:56"
+        _assert_time_sync_in_window(time_sync_response.json()["data"]["time_sync"], before_time_sync, after_time_sync)
     finally:
         platform_service.device_client = old_client
         platform_service.config_repo = old_repo
@@ -257,7 +266,9 @@ def test_protocol_config_endpoints_read_and_write_device_only(tmp_path) -> None:
             headers=headers,
             json={"time_sync": "2026-05-25 14:00:00"},
         )
+        before_query_time_sync = datetime.now()
         query_time_sync = client.get("/api/config/time-sync", headers=headers)
+        after_query_time_sync = datetime.now()
 
         assert channel_response.status_code == 200
         assert line_response.status_code == 200
@@ -271,7 +282,8 @@ def test_protocol_config_endpoints_read_and_write_device_only(tmp_path) -> None:
         assert query_system.json()["data"]["brightness"] == 88
         assert query_net.json()["data"]["ip"] == "172.16.2.10"
         assert query_net.json()["data"]["gateway"] == "172.16.2.1"
-        assert query_time_sync.json()["data"]["time_sync"] == "2026-05-25 14:00:00"
+        assert time_sync_response.json()["data"]["time_sync"] == "2026-05-25 14:00:00"
+        _assert_time_sync_in_window(query_time_sync.json()["data"]["time_sync"], before_query_time_sync, after_query_time_sync)
         assert platform_service.config_repo.read_setting_config() == {}
         assert platform_service.config_repo.read_device_config() == {}
     finally:
@@ -279,6 +291,31 @@ def test_protocol_config_endpoints_read_and_write_device_only(tmp_path) -> None:
         platform_service.config_repo = old_repo
 
 
+def test_mock_time_sync_ws_payload_uses_system_time() -> None:
+    old_client = platform_service.device_client
+    platform_service.device_client = MockDeviceClient()
+    captured: dict = {}
+
+    async def fake_broadcast(channel: str, payload: dict) -> None:
+        captured["channel"] = channel
+        captured["payload"] = payload
+
+    original_broadcast = ws_manager.broadcast
+    ws_manager.broadcast = fake_broadcast
+
+    try:
+        before = datetime.now()
+        asyncio.run(platform_service.poll_time_sync_once())
+        after = datetime.now()
+    finally:
+        ws_manager.broadcast = original_broadcast
+        platform_service.device_client = old_client
+
+    assert captured["channel"] == "time-sync"
+    assert captured["payload"]["type"] == "time_sync"
+    _assert_time_sync_in_window(captured["payload"]["data"]["time_sync"], before, after)
+
+
 def test_save_device_net_and_uart_by_key(tmp_path) -> None:
     old_repo = platform_service.config_repo
     old_client = platform_service.device_client