diff --git a/pipeline_service/llm_proxy.py b/pipeline_service/llm_proxy.py
index 877691b..cc1c2a0 100644
--- a/pipeline_service/llm_proxy.py
+++ b/pipeline_service/llm_proxy.py
@@ -36,6 +36,51 @@ S_REVOKED = "revoked"
 DEFAULT_TTL_HOURS = 8
 DEFAULT_MAX_CALLS = 500
 
+# 失败限速：防 token 枚举。按来源标识（token 前缀/调用方）计数，
+# 窗口内失败次数超阈值则直接拒绝，不再查库（避免枚举放大 DB 压力）。
+_FAIL_WINDOW_SEC = 300
+_FAIL_MAX = 20
+_fail_counters: dict = {}
+
+
+def _fail_key(token):
+    """限速键：取 token 前 12 字符（足够区分调用方，又不在内存留全量密钥）。"""
+    t = (token or '').strip()
+    if t.lower().startswith('bearer '):
+        t = t[7:].strip()
+    return t[:12] or 'anon'
+
+
+def _rate_limited(token):
+    """是否已被限速。顺带清理过期窗口。"""
+    import time
+    now = time.time()
+    k = _fail_key(token)
+    rec = _fail_counters.get(k)
+    if not rec:
+        return False
+    start, cnt = rec
+    if now - start > _FAIL_WINDOW_SEC:
+        _fail_counters.pop(k, None)
+        return False
+    return cnt >= _FAIL_MAX
+
+
+def _record_fail(token):
+    """记一次鉴权失败。"""
+    import time
+    now = time.time()
+    k = _fail_key(token)
+    rec = _fail_counters.get(k)
+    if not rec or now - rec[0] > _FAIL_WINDOW_SEC:
+        _fail_counters[k] = (now, 1)
+    else:
+        _fail_counters[k] = (rec[0], rec[1] + 1)
+    # 防内存膨胀：条目过多时清理已过期窗口
+    if len(_fail_counters) > 5000:
+        for kk in [x for x, v in _fail_counters.items() if now - v[0] > _FAIL_WINDOW_SEC]:
+            _fail_counters.pop(kk, None)
+
 
 def _get_db():
     db = DBPools()
@@ -214,8 +259,13 @@ async def proxy_chat_completion(token, payload):
     返回 (True, 上游响应 dict) 或 (False, 错误信息)。
     真 api_key 由 llm_bridge 按 token 绑定的 org_id 从 llm 表解析，不下发给调用方。
     """
+    # 失败限速前置：窗口内鉴权失败过多直接拒绝（防 token 枚举）
+    if _rate_limited(token):
+        logger.warning("proxy_chat_completion: 限速拒绝 key=%s", _fail_key(token))
+        return False, "鉴权失败次数过多，请稍后再试"
     ok, info = await verify_llm_token(token)
     if not ok:
+        _record_fail(token)
         return False, info
     if not isinstance(payload, dict) or not payload.get('messages'):
         return False, "请求体缺 messages"