diff --git a/frontend/src/App.vue b/frontend/src/App.vue
index dc28964..3641b16 100644
--- a/frontend/src/App.vue
+++ b/frontend/src/App.vue
@@ -10,6 +10,14 @@
         </span>
       </div>
       <div class="flex items-center gap-3 text-xs text-slate-600">
+        <button
+          type="button"
+          class="theme-toggle"
+          :title="`当前主题：${themeModeText}`"
+          @click="cycleThemeMode"
+        >
+          {{ themeModeText }}
+        </button>
         <StatusDot :status="statusDot">
           {{ statusLabel }}
         </StatusDot>
@@ -26,8 +34,30 @@
 import { computed } from 'vue';
 import StatusDot from '@/components/ui/StatusDot.vue';
 import { useWsStore } from '@/stores/wsStore';
+import { useTheme, type ThemeMode } from '@/composables/useTheme';
 
 const wsStore = useWsStore();
+const { themeMode, setThemeMode } = useTheme();
+
+const THEME_ORDER: ThemeMode[] = ['system', 'dark', 'light'];
+
+const themeModeText = computed(() => {
+  switch (themeMode.value) {
+    case 'dark':
+      return '深色';
+    case 'light':
+      return '浅色';
+    case 'system':
+    default:
+      return '跟随系统';
+  }
+});
+
+function cycleThemeMode(): void {
+  const currentIndex = THEME_ORDER.indexOf(themeMode.value);
+  const nextIndex = (currentIndex + 1) % THEME_ORDER.length;
+  setThemeMode(THEME_ORDER[nextIndex]);
+}
 
 const statusDot = computed(() => {
   switch (wsStore.status) {
@@ -57,4 +87,3 @@ const statusLabel = computed(() => {
   }
 });
 </script>
-
diff --git a/frontend/src/assets/main.css b/frontend/src/assets/main.css
index 10b7f1b..90a5cba 100644
--- a/frontend/src/assets/main.css
+++ b/frontend/src/assets/main.css
@@ -32,4 +32,76 @@ body {
 .fade-enter-from,
 .fade-leave-to {
   opacity: 0;
-}
\ No newline at end of file
+}
+
+.theme-toggle {
+  @apply inline-flex items-center px-2.5 h-7 rounded-[var(--dt-radius-btn)] border border-slate-300 bg-white text-slate-700 transition;
+}
+
+.theme-toggle:hover {
+  @apply border-slate-400 bg-slate-50;
+}
+
+html.dark body {
+  color: rgb(241 245 249);
+  background-color: rgb(2 6 23);
+}
+
+html.dark .bg-white {
+  background-color: rgb(15 23 42);
+}
+
+html.dark .bg-white\/80 {
+  background-color: rgb(15 23 42 / 0.8);
+}
+
+html.dark .bg-slate-50 {
+  background-color: rgb(15 23 42);
+}
+
+html.dark .bg-slate-100\/80 {
+  background-color: rgb(15 23 42 / 0.8);
+}
+
+html.dark .text-slate-900 {
+  color: rgb(241 245 249);
+}
+
+html.dark .text-slate-700 {
+  color: rgb(226 232 240);
+}
+
+html.dark .text-slate-600 {
+  color: rgb(203 213 225);
+}
+
+html.dark .text-slate-500 {
+  color: rgb(148 163 184);
+}
+
+html.dark .border-slate-200 {
+  border-color: rgb(51 65 85);
+}
+
+html.dark .border-slate-300 {
+  border-color: rgb(71 85 105);
+}
+
+html.dark .border-dashed {
+  border-style: dashed;
+}
+
+html.dark .placeholder\:text-slate-400::placeholder {
+  color: rgb(148 163 184);
+}
+
+html.dark .theme-toggle {
+  border-color: rgb(71 85 105);
+  background-color: rgb(30 41 59);
+  color: rgb(226 232 240);
+}
+
+html.dark .theme-toggle:hover {
+  border-color: rgb(100 116 139);
+  background-color: rgb(51 65 85);
+}
diff --git a/frontend/src/composables/useTheme.ts b/frontend/src/composables/useTheme.ts
new file mode 100644
index 0000000..ac9fa13
--- /dev/null
+++ b/frontend/src/composables/useTheme.ts
@@ -0,0 +1,87 @@
+import { computed, readonly, ref } from 'vue';
+
+type ResolvedTheme = 'light' | 'dark';
+export type ThemeMode = 'system' | 'light' | 'dark';
+
+const STORAGE_KEY = 'DataTool-theme-mode';
+
+const themeMode = ref<ThemeMode>(loadThemeMode());
+const resolvedTheme = ref<ResolvedTheme>('light');
+
+let mediaQuery: MediaQueryList | null = null;
+let initialized = false;
+
+function loadThemeMode(): ThemeMode {
+  if (typeof window === 'undefined') {
+    return 'system';
+  }
+  const saved = window.localStorage.getItem(STORAGE_KEY);
+  if (saved === 'light' || saved === 'dark' || saved === 'system') {
+    return saved;
+  }
+  return 'system';
+}
+
+function getSystemTheme(): ResolvedTheme {
+  if (typeof window === 'undefined' || typeof window.matchMedia !== 'function') {
+    return 'light';
+  }
+  return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
+}
+
+function applyTheme(theme: ResolvedTheme): void {
+  if (typeof document === 'undefined') {
+    return;
+  }
+  const root = document.documentElement;
+  root.classList.toggle('dark', theme === 'dark');
+  root.style.colorScheme = theme;
+}
+
+function resolveTheme(mode: ThemeMode): ResolvedTheme {
+  if (mode === 'system') {
+    return getSystemTheme();
+  }
+  return mode;
+}
+
+function syncTheme(): void {
+  const next = resolveTheme(themeMode.value);
+  resolvedTheme.value = next;
+  applyTheme(next);
+}
+
+function ensureInit(): void {
+  if (initialized || typeof window === 'undefined') {
+    return;
+  }
+  initialized = true;
+  mediaQuery = window.matchMedia('(prefers-color-scheme: dark)');
+  mediaQuery.addEventListener('change', () => {
+    if (themeMode.value === 'system') {
+      syncTheme();
+    }
+  });
+  syncTheme();
+}
+
+function setThemeMode(nextMode: ThemeMode): void {
+  themeMode.value = nextMode;
+  if (typeof window !== 'undefined') {
+    window.localStorage.setItem(STORAGE_KEY, nextMode);
+  }
+  syncTheme();
+}
+
+export function useTheme() {
+  ensureInit();
+
+  const isDark = computed(() => resolvedTheme.value === 'dark');
+
+  return {
+    themeMode: readonly(themeMode),
+    resolvedTheme: readonly(resolvedTheme),
+    isDark,
+    setThemeMode,
+  };
+}