diff --git a/plugins/op_waf/waf/lua/common.lua b/plugins/op_waf/waf/lua/common.lua
index f477fdbd6..09a2fa527 100644
--- a/plugins/op_waf/waf/lua/common.lua
+++ b/plugins/op_waf/waf/lua/common.lua
@@ -44,15 +44,17 @@ end
 function _M.getInstance(self)
     if rawget(self, "instance") == nil then
         rawset(self, "instance", self:new())
-
-        if 0 == ngx.worker.id() then
-            self:cron()
-        end
     end
     assert(self.instance ~= nil)
     return self.instance
 end
 
+function _M:initCron(self)
+    if 0 == ngx.worker.id() then
+        self:cron()
+    end
+end
+
 function _M.initDB(self)
     local path = log_dir .. "/waf.db"
     db, err = sqlite3.open(path)
diff --git a/plugins/op_waf/waf/lua/init_worker.lua b/plugins/op_waf/waf/lua/init_worker.lua
index 5bf722c9d..172a8532a 100644
--- a/plugins/op_waf/waf/lua/init_worker.lua
+++ b/plugins/op_waf/waf/lua/init_worker.lua
@@ -15,6 +15,9 @@ local json = require "cjson"
 local __C = require "common"
 local C = __C:getInstance()
 
+-- cron
+C:initCron()
+
 local function timer_stats_total_log(premature)
     C:timer_stats_total()
 end