diff --git a/captcha/README.md b/captcha/README.md
index 43376d7..0b388f4 100644
--- a/captcha/README.md
+++ b/captcha/README.md
@@ -6,7 +6,7 @@
 
 ## 功能特性
 
-- **图片验证码生成**：5 位字符（字母 + 数字），自动排除易混淆字符（`l I 1 O 0 o`）
+- **图片验证码生成**：4 位字符（字母 + 数字），自动排除易混淆字符（`l I 1 O 0 o`）
 - **Token 机制**：每次生成图片返回唯一 Token（32 位十六进制），校验时**一次性消费**，防止重放
 - **过期自动清理**：Token 默认 300 秒（5 分钟）失效；`image` 路由请求时顺带清理过期项
 - **线程安全**：使用锁（`STORE_LOCK`）保护内存存储，支持并发请求
diff --git a/captcha/captcha_service.py b/captcha/captcha_service.py
index 009cb8a..054749b 100644
--- a/captcha/captcha_service.py
+++ b/captcha/captcha_service.py
@@ -38,7 +38,7 @@ from pymsg import MsgServer  # noqa: E402
 
 # ── 配置 ────────────────────────────────────────────────────────────────
 
-CAPTCHA_LEN = 5
+CAPTCHA_LEN = 4
 CAPTCHA_TTL = 300        # Token 有效期（秒）
 
 CHARS = string.ascii_letters + string.digits
@@ -63,7 +63,7 @@ def generate_image(text):
     for i, ch in enumerate(text):
         color = random.choice([(30, 30, 30), (50, 80, 150), (150, 50, 50), (50, 130, 50)])
         y = random.randint(2, 12)
-        x = 10 + i * 28 + random.randint(-3, 3)
+        x = 15 + i * 32 + random.randint(-3, 3)   # 4 位字符在 160px 宽度内均匀分布
         try:
             font = ImageFont.truetype("/usr/share/fonts/truetype/dejavu/DejaVuSans-Bold.ttf",
                                       random.choice([28, 30, 32, 34]))
diff --git a/static/public/login.html b/static/public/login.html
index e0438a4..41af9e4 100644
--- a/static/public/login.html
+++ b/static/public/login.html
@@ -18,8 +18,8 @@
 					<input type="password" id="loginPassword" placeholder="请输入密码">
 					<span id="pwdTip"></span>
 					<label>验证码：</label>
-					<input type="text" id="captchaAnswer" placeholder="请输入验证码" maxlength="5" autocomplete="off" style="width:110px">
-					<img id="captchaImg" alt="加载中…" title="点击刷新验证码" style="width:120px;height:38px;vertical-align:middle;cursor:pointer;margin-left:8px;border:1px solid #ddd;border-radius:4px;box-sizing:border-box">
+					<img id="captchaImg" alt="加载中…" title="点击刷新验证码" style="width:120px;height:38px;vertical-align:middle;cursor:pointer;margin-right:8px;border:1px solid #ddd;border-radius:4px;box-sizing:border-box">
+					<input type="text" id="captchaAnswer" placeholder="请输入验证码" maxlength="4" autocomplete="off" style="width:110px">
 					<span id="captchaTip"></span>
 				</div>
 				<div class="form-actions">