diff --git a/apisix/plugins/limit-conn/limit-conn-redis-cluster.lua b/apisix/plugins/limit-conn/limit-conn-redis-cluster.lua
index 9295238724b3..9e46a04b2181 100644
--- a/apisix/plugins/limit-conn/limit-conn-redis-cluster.lua
+++ b/apisix/plugins/limit-conn/limit-conn-redis-cluster.lua
@@ -16,10 +16,8 @@
 --
 local redis_cluster     = require("apisix.utils.rediscluster")
 local core              = require("apisix.core")
-local assert            = assert
+local util              = require("apisix.plugins.limit-conn.util")
 local setmetatable      = setmetatable
-local math              = require "math"
-local floor             = math.floor
 local ngx_timer_at      = ngx.timer.at
 
 local _M = {version = 0.1}
@@ -49,44 +47,7 @@ end
 
 
 function _M.incoming(self, key, commit)
-    local max = self.max
-    local red = self.red_cli
-
-    self.committed = false
-
-    local hash_key = "limit_conn"
-
-    local conn, err
-    if commit then
-        conn, err = red:hincrby(hash_key, key, 1)
-        if not conn then
-            return nil, err
-        end
-
-        if conn > max + self.burst then
-            conn, err = red:hincrby(hash_key, key, -1)
-            if not conn then
-                return nil, err
-            end
-            return nil, "rejected"
-        end
-        self.committed = true
-
-    else
-        local conn_from_red, err = red:hget(hash_key, key)
-        if err then
-            return nil, err
-        end
-        conn = (conn_from_red or 0) + 1
-    end
-
-    if conn > max then
-        -- make the excessive connections wait
-        return self.unit_delay * floor((conn - 1) / max), conn
-    end
-
-    -- we return a 0 delay by default
-    return 0, conn
+    return util.incoming(self, self.red_cli, key, commit)
 end
 
 
@@ -96,28 +57,11 @@ end
 
 
 local function leaving_thread(premature, self, key, req_latency)
-
-    local red = self.red_cli
-
-    local hash_key = "limit_conn"
-
-    local conn, err = red:hincrby(hash_key, key, -1)
-    if not conn then
-        return nil, err
-    end
-
-    if req_latency then
-        local unit_delay = self.unit_delay
-        self.unit_delay = (req_latency + unit_delay) / 2
-    end
-
-    return conn
+    return util.leaving(self, self.red_cli, key, req_latency)
 end
 
 
 function _M.leaving(self, key, req_latency)
-    assert(key)
-
     -- log_by_lua can't use cosocket
     local ok, err = ngx_timer_at(0, leaving_thread, self, key, req_latency)
     if not ok then
diff --git a/apisix/plugins/limit-conn/limit-conn-redis.lua b/apisix/plugins/limit-conn/limit-conn-redis.lua
index e8a3861d7529..4de7a27fdca2 100644
--- a/apisix/plugins/limit-conn/limit-conn-redis.lua
+++ b/apisix/plugins/limit-conn/limit-conn-redis.lua
@@ -14,11 +14,9 @@
 -- See the License for the specific language governing permissions and
 -- limitations under the License.
 --
-local redis     = require("apisix.utils.redis")
+local redis         = require("apisix.utils.redis")
 local core          = require("apisix.core")
-local assert        = assert
-local math          = require "math"
-local floor         = math.floor
+local util          = require("apisix.plugins.limit-conn.util")
 local ngx_timer_at  = ngx.timer.at
 
 local setmetatable  = setmetatable
@@ -45,49 +43,12 @@ end
 
 
 function _M.incoming(self, key, commit)
-    local max = self.max
-
     local conf = self.conf
     local red, err = redis.new(conf)
     if not red then
         return red, err
     end
-
-    self.committed = false
-
-    local hash_key = "limit_conn"
-
-    local conn, err
-    if commit then
-        conn, err = red:hincrby(hash_key, key, 1)
-        if not conn then
-            return nil, err
-        end
-
-        if conn > max + self.burst then
-            conn, err = red:hincrby(hash_key, key, -1)
-            if not conn then
-                return nil, err
-            end
-            return nil, "rejected"
-        end
-        self.committed = true
-
-    else
-        local conn_from_red, err = red:hget(hash_key, key)
-        if err then
-            return nil, err
-        end
-        conn = (conn_from_red or 0) + 1
-    end
-
-    if conn > max then
-        -- make the excessive connections wait
-        return self.unit_delay * floor((conn - 1) / max), conn
-    end
-
-    -- we return a 0 delay by default
-    return 0, conn
+    return util.incoming(self, red, key, commit)
 end
 
 
@@ -103,26 +64,11 @@ local function leaving_thread(premature, self, key, req_latency)
     if not red then
         return red, err
     end
-
-    local hash_key = "limit_conn"
-
-    local conn, err = red:hincrby(hash_key, key, -1)
-    if not conn then
-        return nil, err
-    end
-
-    if req_latency then
-        local unit_delay = self.unit_delay
-        self.unit_delay = (req_latency + unit_delay) / 2
-    end
-
-    return conn
+    return util.leaving(self, red, key, req_latency)
 end
 
 
 function _M.leaving(self, key, req_latency)
-    assert(key)
-
     -- log_by_lua can't use cosocket
     local ok, err = ngx_timer_at(0, leaving_thread, self, key, req_latency)
     if not ok then
diff --git a/apisix/plugins/limit-conn/util.lua b/apisix/plugins/limit-conn/util.lua
new file mode 100644
index 000000000000..0142482ba09e
--- /dev/null
+++ b/apisix/plugins/limit-conn/util.lua
@@ -0,0 +1,84 @@
+--
+-- Licensed to the Apache Software Foundation (ASF) under one or more
+-- contributor license agreements.  See the NOTICE file distributed with
+-- this work for additional information regarding copyright ownership.
+-- The ASF licenses this file to You under the Apache License, Version 2.0
+-- (the "License"); you may not use this file except in compliance with
+-- the License.  You may obtain a copy of the License at
+--
+--     http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS,
+-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+-- See the License for the specific language governing permissions and
+-- limitations under the License.
+--
+
+local core = require("apisix.core")
+
+local assert            = assert
+local math              = require "math"
+local floor             = math.floor
+local _M = {version = 0.3}
+
+
+function _M.incoming(self, red, key, commit)
+    local max = self.max
+    self.committed = false
+    local hash_key = "limit_conn"
+
+    local conn, err
+    if commit then
+        conn, err = red:hincrby(hash_key, key, 1)
+        if not conn then
+            return nil, err
+        end
+
+        if conn > max + self.burst then
+            conn, err = red:hincrby(hash_key, key, -1)
+            if not conn then
+                return nil, err
+            end
+            return nil, "rejected"
+        end
+        self.committed = true
+
+    else
+        local conn_from_red, err = red:hget(hash_key, key)
+        if err then
+            return nil, err
+        end
+        conn = (conn_from_red or 0) + 1
+    end
+
+    if conn > max then
+        -- make the excessive connections wait
+        return self.unit_delay * floor((conn - 1) / max), conn
+    end
+
+    -- we return a 0 delay by default
+    return 0, conn
+end
+
+
+
+function _M.leaving(self, red, key, req_latency)
+    assert(key)
+    local hash_key = "limit_conn"
+
+    local conn, err = red:hincrby(hash_key, key, -1)
+    if not conn then
+        return nil, err
+    end
+
+    if req_latency then
+        local unit_delay = self.unit_delay
+        self.unit_delay = (req_latency + unit_delay) / 2
+    end
+
+    return conn
+end
+
+
+return _M