diff --git a/backend/server.js b/backend/server.js
index 3d20dee..a526e50 100644
--- a/backend/server.js
+++ b/backend/server.js
@@ -436,6 +436,46 @@ const shareLimiter = new RateLimiter({
   blockDuration: 20 * 60 * 1000
 });
 
+// 创建验证码获取限流器（30次请求/10分钟，封锁30分钟）
+const captchaLimiter = new RateLimiter({
+  maxAttempts: 30,
+  windowMs: 10 * 60 * 1000,
+  blockDuration: 30 * 60 * 1000
+});
+
+// 验证码最小请求间隔控制
+const CAPTCHA_MIN_INTERVAL = 3000; // 3秒
+const captchaLastRequest = new TTLCache(15 * 60 * 1000); // 15分钟自动清理
+
+// 验证码防刷中间件
+function captchaRateLimitMiddleware(req, res, next) {
+  const clientKey = `captcha:${captchaLimiter.getClientKey(req)}`;
+  const now = Date.now();
+
+  // 最小时间间隔限制
+  const lastRequest = captchaLastRequest.get(clientKey);
+  if (lastRequest && (now - lastRequest) < CAPTCHA_MIN_INTERVAL) {
+    return res.status(429).json({
+      success: false,
+      message: '验证码请求过于频繁，请稍后再试'
+    });
+  }
+  captchaLastRequest.set(clientKey, now, 15 * 60 * 1000);
+
+  // 窗口内总次数限流
+  const result = captchaLimiter.recordFailure(clientKey);
+  if (result.blocked) {
+    return res.status(429).json({
+      success: false,
+      message: `验证码请求过多，请在 ${result.waitMinutes} 分钟后再试`,
+      blocked: true,
+      resetTime: result.resetTime
+    });
+  }
+
+  next();
+}
+
 // 登录防爆破中间件
 function loginRateLimitMiddleware(req, res, next) {
   const clientIP = loginLimiter.getClientKey(req);
@@ -601,17 +641,17 @@ app.get('/api/health', (req, res) => {
 });
 
 // 生成验证码API
-app.get('/api/captcha', (req, res) => {
+app.get('/api/captcha', captchaRateLimitMiddleware, (req, res) => {
   try {
     const captcha = svgCaptcha.create({
-      size: 4, // 验证码长度
-      noise: 2, // 干扰线条数
+      size: 6, // 验证码长度
+      noise: 3, // 干扰线条数
       color: true, // 使用彩色
-      background: '#f0f0f0', // 背景色
-      width: 120,
-      height: 40,
-      fontSize: 50,
-      charPreset: '0123456789' // 只使用数字
+      background: '#f7f7f7', // 背景色
+      width: 140,
+      height: 44,
+      fontSize: 52,
+      charPreset: 'ABCDEFGHJKLMNPQRSTUVWXYZ23456789' // 去掉易混淆字符，字母+数字
     });
 
     // 将验证码文本存储在session中