diff --git a/client/src/ui_main.py b/client/src/ui_main.py
index 81eb4d3..89cac5f 100644
--- a/client/src/ui_main.py
+++ b/client/src/ui_main.py
@@ -148,7 +148,7 @@ def ui_main():
     setTheme(Theme.AUTO)
 
     window = MainWindow()
-    window.show()
+    window.showMaximized()
     try:
         mark_current_version_healthy()
     except OSError:
diff --git a/client/test/test_pdd_ui_event.py b/client/test/test_pdd_ui_event.py
index e6ce4ec..c1eb0eb 100644
--- a/client/test/test_pdd_ui_event.py
+++ b/client/test/test_pdd_ui_event.py
@@ -42,7 +42,7 @@ from src.task_models import (
     TaskType,
 )
 from src.task_repository import TaskRepository
-from src.ui_main import MainWindow
+from src.ui_main import MainWindow, ui_main
 
 
 class BrokenRepository:
@@ -1144,6 +1144,36 @@ class PDDTaskPageEventTest(unittest.TestCase):
         window.close()
         window.deleteLater()
 
+    def test_application_startup_shows_main_window_maximized(self):
+        class FakeApplication:
+            @staticmethod
+            def setAttribute(*_args):
+                pass
+
+            def __init__(self, _args):
+                pass
+
+            def exec_(self):
+                return 0
+
+        class FakeWindow:
+            def __init__(self):
+                self.maximized = False
+
+            def showMaximized(self):
+                self.maximized = True
+
+        window = FakeWindow()
+        with patch("src.ui_main.QApplication", FakeApplication), patch(
+            "src.ui_main.MainWindow", return_value=window
+        ), patch("src.ui_main.setTheme"), patch(
+            "src.ui_main.mark_current_version_healthy"
+        ):
+            result = ui_main()
+
+        self.assertEqual(result, 0)
+        self.assertTrue(window.maximized)
+
     def test_main_window_marks_and_clears_update_navigation(self):
         window = MainWindow(
             task_repository=self.repository,
diff --git a/docs/client/05-ui-specification.md b/docs/client/05-ui-specification.md
index 8273e47..edbf64c 100644
--- a/docs/client/05-ui-specification.md
+++ b/docs/client/05-ui-specification.md
@@ -32,7 +32,9 @@
 
 > **现状提醒：** 当前代码里是 3 个导航项（pdd / 设备 / 设置），和这里写的 2 个不一样。这是已知差异，见 [02 架构 §3.1](02-architecture.md)。设备相关设置最终要并入设置页，但要按工单单独做，不要顺手改。
 
-窗口建议默认尺寸为 1280×800，有效最小尺寸不低于 960×600。窗口变窄时允许表格水平滚动和顶部命令换行，不能隐藏主要任务入口。
+Client 首次显示主窗口时使用标准 Windows 最大化状态，不使用全屏模式。用户仍可通过标题栏
+最小化、还原、调整大小、再次最大化或关闭窗口。窗口变窄时允许表格水平滚动和顶部命令
+换行，不能隐藏主要任务入口。
 
 ## 3. PDD 任务页布局