diff --git a/app/composables/useSiteConfig.js b/app/composables/useSiteConfig.js
index fcc8598..4c635a6 100644
--- a/app/composables/useSiteConfig.js
+++ b/app/composables/useSiteConfig.js
@@ -62,8 +62,8 @@ export const useSiteConfig = () => {
         enableReplayRequests: false,
         enableCollaborativeSubmission: true,
         enableSubmissionRemarks: false,
-        defaultTheme: 'ClassicLight',
-        enabledThemes: '["ClassicLight","ModernLight"]',
+        defaultTheme: 'ClassicDark',
+        enabledThemes: '["System","ClassicDark","ClassicLight","ModernLight"]',
         statisticsCode: '',
         statisticsCodeEnabled: false
       }
diff --git a/app/drizzle/schema.ts b/app/drizzle/schema.ts
index 4399622..2e1579f 100644
--- a/app/drizzle/schema.ts
+++ b/app/drizzle/schema.ts
@@ -350,8 +350,8 @@ export const systemSettings = pgTable('SystemSettings', {
   autoBackupConfig: text('autoBackupConfig'),
   statisticsCode: text('statisticsCode'),
   statisticsCodeEnabled: boolean('statisticsCodeEnabled').default(false).notNull(),
-  defaultTheme: text('defaultTheme').default('ClassicLight').notNull(),
-  enabledThemes: text('enabledThemes').default('[\"ClassicLight\",\"ModernLight\"]').notNull(),
+  defaultTheme: text('defaultTheme').default('ClassicDark').notNull(),
+  enabledThemes: text('enabledThemes').default('[\"System\",\"ClassicDark\",\"ClassicLight\",\"ModernLight\"]').notNull(),
   enabledPlatforms: text('enabledPlatforms'),
   platformOrder: text('platformOrder'),
 });
diff --git a/app/pages/index.vue b/app/pages/index.vue
index 7ec75dd..62f57c8 100644
--- a/app/pages/index.vue
+++ b/app/pages/index.vue
@@ -33,18 +33,6 @@
         <!-- 用户信息区域 -->
         <div class="user-section">
           <ClientOnly>
-            <!-- 主题切换按钮 -->
-            <button
-              class="utility-btn theme-toggle-btn"
-              type="button"
-              aria-label="主题"
-              title="切换主题"
-              @click="handleToggleTheme"
-            >
-              <Icon :name="isDark ? 'sun' : 'moon'" :size="18" />
-              <span class="utility-btn-label">主题</span>
-            </button>
-
             <div v-if="isClientAuthenticated" class="user-info">
               <div class="user-details-desktop">
                 <span class="user-name">{{ user?.name || '用户' }}</span>
@@ -686,19 +674,12 @@ import ConfirmDialog from '~/components/UI/ConfirmDialog.vue'
 
 import { useNotifications } from '~/composables/useNotifications'
 import { useSiteConfig } from '~/composables/useSiteConfig'
-import { useTheme } from '~/composables/useTheme'
 import CustomSelect from '~/components/UI/Common/CustomSelect.vue'
 
 // 获取运行时配置
 const config = useRuntimeConfig()
 const router = useRouter()
 
-// 主题
-const { isDark, toggleTheme } = useTheme()
-const handleToggleTheme = () => {
-  toggleTheme()
-}
-
 // 站点配置
 const {
   siteTitle,
diff --git a/nuxt.config.ts b/nuxt.config.ts
index d5ff5f3..f0eefe7 100644
--- a/nuxt.config.ts
+++ b/nuxt.config.ts
@@ -156,8 +156,8 @@ export default defineNuxtConfig({
         themeColor: process.env.PWA_THEME_COLOR || '#111111'
       },
       // 主题配置
-      defaultTheme: process.env.NUXT_PUBLIC_DEFAULT_THEME || 'ClassicLight',
-      enabledThemes: (process.env.NUXT_PUBLIC_ENABLED_THEMES || 'ClassicLight,ModernLight')
+      defaultTheme: process.env.NUXT_PUBLIC_DEFAULT_THEME || 'ClassicDark',
+      enabledThemes: (process.env.NUXT_PUBLIC_ENABLED_THEMES || 'System,ClassicDark,ClassicLight,ModernLight')
         .split(',')
         .map((s) => s.trim())
         .filter(Boolean),
@@ -192,7 +192,7 @@ export default defineNuxtConfig({
         { name: 'theme-color', content: '#111111' },
         {
           name: 'x-default-theme',
-          content: process.env.NUXT_PUBLIC_DEFAULT_THEME || 'ClassicLight'
+          content: process.env.NUXT_PUBLIC_DEFAULT_THEME || 'ClassicDark'
         },
         { name: 'apple-mobile-web-app-capable', content: 'yes' },
         { name: 'apple-mobile-web-app-status-bar-style', content: 'black-translucent' },
@@ -213,7 +213,7 @@ export default defineNuxtConfig({
             `      var meta=document.querySelector('meta[name="x-default-theme"]');`,
             `      if(meta && meta.content){s=meta.content}`,
             `    }catch(e){s=null}`,
-            `    if(!s){s='ClassicLight'}`,
+            `    if(!s){s='ClassicDark'}`,
             `  }`,
             `  if(s==='System'||s==='system'){eff=window.matchMedia('(prefers-color-scheme: dark)').matches?'dark':'light'}`,
             `  else if(typeof s==='string'){eff=s.endsWith('Dark')||s==='dark'?'dark':(s.endsWith('Light')||s==='light'?'light':s)}`,
diff --git a/server/api/admin/system-settings/index.post.ts b/server/api/admin/system-settings/index.post.ts
index 1c25235..6c79a57 100644
--- a/server/api/admin/system-settings/index.post.ts
+++ b/server/api/admin/system-settings/index.post.ts
@@ -833,8 +833,8 @@ export default defineEventHandler(async (event) => {
   autoBackupIntervalHours: 24,
   autoBackupRetentionDays: 30,
   statisticsCodeEnabled: false,
-  defaultTheme: 'ClassicLight',
-  enabledThemes: '["ClassicLight","ModernLight"]'
+  defaultTheme: 'ClassicDark',
+  enabledThemes: '["System","ClassicDark","ClassicLight","ModernLight"]'
 } as const
 
     // 获取当前设置，如果不存在则创建
diff --git a/server/api/site-config.get.ts b/server/api/site-config.get.ts
index 0ad6af9..a22335c 100644
--- a/server/api/site-config.get.ts
+++ b/server/api/site-config.get.ts
@@ -90,8 +90,8 @@ export default defineEventHandler(async (event) => {
           forceBlockAllRequests: false,
           enableReplayRequests: false,
           smtpEnabled: false,
-          defaultTheme: 'ClassicLight',
-          enabledThemes: '["ClassicLight","ModernLight"]',
+          defaultTheme: 'ClassicDark',
+          enabledThemes: '["System","ClassicDark","ClassicLight","ModernLight"]',
           scheduleDaysBeforeEnabled: false,
           scheduleDaysBefore: 30,
           scheduleDaysAfterEnabled: false,
diff --git a/server/utils/system-settings-defaults.ts b/server/utils/system-settings-defaults.ts
index 73e2251..c317556 100644
--- a/server/utils/system-settings-defaults.ts
+++ b/server/utils/system-settings-defaults.ts
@@ -68,6 +68,6 @@ export const SYSTEM_SETTINGS_DEFAULTS = {
   autoBackupRetentionDays: 30,
   statisticsCode: '',
   statisticsCodeEnabled: false,
-  defaultTheme: 'ClassicLight',
-  enabledThemes: '["ClassicLight","ModernLight"]'
+  defaultTheme: 'ClassicDark',
+  enabledThemes: '["System","ClassicDark","ClassicLight","ModernLight"]'
 } as const