diff --git a/server/imserver/dbhelper.cc b/server/imserver/dbhelper.cc
index 9e30918..edd2cf7 100644
--- a/server/imserver/dbhelper.cc
+++ b/server/imserver/dbhelper.cc
@@ -1,6 +1,7 @@
 #include "precompile.h"
 
 #include <a8/openssl.h>
+#include <a8/timer.h>
 
 #include "dbengine.h"
 
@@ -280,5 +281,45 @@ void DBHelper::AddCache(
         user_info->mutable_base_data()->set__online(0);
         cache_users_hash[account_id] = user_info;
         cache_users_list.push_back(user_info);
+        a8::Timer::Instance()->AddDeadLineTimer
+            (
+             1000 * 60 * 5 + rand() % 1000,
+             a8::XParams()
+             .SetSender(account_id),
+             [] (const a8::XParams& param)
+             {
+                 DBHelper::Instance()->RemoveCache(param.sender);
+             }
+             );
+    }
+}
+
+void DBHelper::RemoveCache(const std::string& account_id)
+{
+    if (cache_users_hash.size() < 300) {
+        a8::Timer::Instance()->AddDeadLineTimer
+            (
+             1000 * 60 * 5 + rand() % 1000,
+             a8::XParams()
+             .SetSender(account_id),
+             [] (const a8::XParams& param)
+             {
+                 DBHelper::Instance()->RemoveCache(param.sender);
+             }
+             );
+        return;
+    }
+    auto itr = cache_users_hash.find(account_id);
+    if (itr != cache_users_hash.end()) {
+        auto itr2 = std::find(cache_users_list.begin(),
+                              cache_users_list.end(),
+                              itr->second);
+        if (itr2 != cache_users_list.end()) {
+            cache_users_list.erase(itr2);
+        } else {
+            abort();
+        }
+        delete itr->second;
+        cache_users_hash.erase(itr);
     }
 }
diff --git a/server/imserver/dbhelper.h b/server/imserver/dbhelper.h
index 32c10c3..6c1daaf 100644
--- a/server/imserver/dbhelper.h
+++ b/server/imserver/dbhelper.h
@@ -54,4 +54,5 @@ private:
                   long long user_value3,
                   int last_logintime
                   );
+    void RemoveCache(const std::string& account_id);
 };