diff --git a/.autod.conf.js b/.autod.conf.js
index cac3312124..a573b24e6d 100644
--- a/.autod.conf.js
+++ b/.autod.conf.js
@@ -26,8 +26,5 @@ module.exports = {
     '@types/koa',
     '@types/koa-router',
   ],
-  semver: [
-    'koa-bodyparser@2',
-  ],
   test: 'scripts',
 };
diff --git a/.travis.yml b/.travis.yml
index 29d6351511..ad743fb435 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,7 +1,6 @@
 sudo: false
 language: node_js
 node_js:
-  - '6'
   - '8'
   - '9'
 install:
diff --git a/app/extend/context.js b/app/extend/context.js
index df9f6a9f76..1597e842bf 100644
--- a/app/extend/context.js
+++ b/app/extend/context.js
@@ -1,7 +1,6 @@
 'use strict';
 
 const delegate = require('delegates');
-const co = require('co');
 const { assign } = require('utility');
 
 const HELPER = Symbol('Context#helper');
@@ -197,13 +196,15 @@ const proto = module.exports = {
     const start = Date.now();
     /* istanbul ignore next */
     const taskName = scope.name || '-';
-    co(function* () {
-      yield scope(ctx);
-      ctx.coreLogger.info('[egg:background] task:%s success (%dms)', taskName, Date.now() - start);
-    }).catch(err => {
-      ctx.coreLogger.info('[egg:background] task:%s fail (%dms)', taskName, Date.now() - start);
-      ctx.coreLogger.error(err);
-    });
+    // use app.toAsyncFunction to support both generator function and async function
+    ctx.app.toAsyncFunction(scope)(ctx)
+      .then(() => {
+        ctx.coreLogger.info('[egg:background] task:%s success (%dms)', taskName, Date.now() - start);
+      })
+      .catch(err => {
+        ctx.coreLogger.info('[egg:background] task:%s fail (%dms)', taskName, Date.now() - start);
+        ctx.coreLogger.error(err);
+      });
   },
 };
 
diff --git a/app/middleware/meta.js b/app/middleware/meta.js
index b0da79186f..efef61c2c9 100644
--- a/app/middleware/meta.js
+++ b/app/middleware/meta.js
@@ -5,9 +5,9 @@
 'use strict';
 
 module.exports = () => {
-  return function* meta(next) {
-    yield next;
+  return async function meta(ctx, next) {
+    await next();
     // total response time header
-    this.set('x-readtime', Date.now() - this.starttime);
+    ctx.set('x-readtime', Date.now() - ctx.starttime);
   };
 };
diff --git a/app/middleware/notfound.js b/app/middleware/notfound.js
index daaf28705b..4ec4288f8e 100644
--- a/app/middleware/notfound.js
+++ b/app/middleware/notfound.js
@@ -1,18 +1,18 @@
 'use strict';
 
 module.exports = options => {
-  return function* notfound(next) {
-    yield next;
+  return async function notfound(ctx, next) {
+    await next();
 
-    if (this.status !== 404 || this.body) {
+    if (ctx.status !== 404 || ctx.body) {
       return;
     }
 
     // set status first, make sure set body not set status
-    this.status = 404;
+    ctx.status = 404;
 
-    if (this.acceptJSON) {
-      this.body = {
+    if (ctx.acceptJSON) {
+      ctx.body = {
         message: 'Not Found',
       };
       return;
@@ -21,16 +21,16 @@ module.exports = options => {
     const notFoundHtml = '<h1>404 Not Found</h1>';
 
     // notfound handler is unimplemented
-    if (options.pageUrl && this.path === options.pageUrl) {
-      this.body = `${notFoundHtml}<p><pre><code>config.notfound.pageUrl(${options.pageUrl})</code></pre> is unimplemented</p>`;
+    if (options.pageUrl && ctx.path === options.pageUrl) {
+      ctx.body = `${notFoundHtml}<p><pre><code>config.notfound.pageUrl(${options.pageUrl})</code></pre> is unimplemented</p>`;
       return;
     }
 
     if (options.pageUrl) {
-      this.realStatus = 404;
-      this.redirect(options.pageUrl);
+      ctx.realStatus = 404;
+      ctx.redirect(options.pageUrl);
       return;
     }
-    this.body = notFoundHtml;
+    ctx.body = notFoundHtml;
   };
 };
diff --git a/app/middleware/site_file.js b/app/middleware/site_file.js
index 2fde8e5746..bca4307727 100644
--- a/app/middleware/site_file.js
+++ b/app/middleware/site_file.js
@@ -4,27 +4,27 @@ const path = require('path');
 const MAX_AGE = 'public, max-age=2592000'; // 30 days
 
 module.exports = options => {
-  return function* siteFile(next) {
-    if (this.method !== 'HEAD' && this.method !== 'GET') return yield next;
+  return function siteFile(ctx, next) {
+    if (ctx.method !== 'HEAD' && ctx.method !== 'GET') return next();
     /* istanbul ignore if */
-    if (this.path[0] !== '/') return yield next;
+    if (ctx.path[0] !== '/') return next();
 
-    const content = options[this.path];
-    if (!content) return yield next;
+    const content = options[ctx.path];
+    if (!content) return next();
 
     // '/favicon.ico': 'https://eggjs.org/favicon.ico',
     // content is url
-    if (typeof content === 'string') return this.redirect(content);
+    if (typeof content === 'string') return ctx.redirect(content);
 
     // '/robots.txt': Buffer <xx..
     // content is buffer
     if (Buffer.isBuffer(content)) {
-      this.set('cache-control', MAX_AGE);
-      this.body = content;
-      this.type = path.extname(this.path);
+      ctx.set('cache-control', MAX_AGE);
+      ctx.body = content;
+      ctx.type = path.extname(ctx.path);
       return;
     }
 
-    yield next;
+    return next();
   };
 };
diff --git a/appveyor.yml b/appveyor.yml
index 0066372735..6c339834b1 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -1,8 +1,7 @@
 environment:
   matrix:
-    - nodejs_version: '6'
-    - nodejs_version: '7'
     - nodejs_version: '8'
+    - nodejs_version: '9'
 
 install:
   - ps: Install-Product node $env:nodejs_version
diff --git a/lib/egg.js b/lib/egg.js
index 905af14352..02b790f077 100644
--- a/lib/egg.js
+++ b/lib/egg.js
@@ -398,11 +398,7 @@ class EggApplication extends EggCore {
     client.create = (...args) => {
       const realClient = create.apply(client, args);
       this[CLUSTER_CLIENTS].push(realClient);
-
-      this.beforeClose(function* () {
-        yield cluster.close(realClient);
-      });
-
+      this.beforeClose(() => cluster.close(realClient));
       return realClient;
     };
   }
diff --git a/package.json b/package.json
index b1217e39d2..3412f7e318 100644
--- a/package.json
+++ b/package.json
@@ -19,12 +19,11 @@
     "accepts": "^1.3.4",
     "agentkeepalive": "^3.3.0",
     "cluster-client": "^1.7.1",
-    "co": "^4.6.0",
     "debug": "^3.1.0",
     "delegates": "^1.0.0",
     "egg-cluster": "^1.12.4",
     "egg-cookies": "^2.2.1",
-    "egg-core": "^3.18.0",
+    "egg-core": "^4.0.0",
     "egg-development": "^1.3.2",
     "egg-i18n": "^1.2.0",
     "egg-jsonp": "^1.2.1",
@@ -42,9 +41,9 @@
     "graceful": "^1.0.1",
     "humanize-ms": "^1.2.1",
     "is-type-of": "^1.2.0",
-    "koa-bodyparser": "^2.5.0",
+    "koa-bodyparser": "^4.2.0",
     "koa-is-json": "^1.0.0",
-    "koa-override": "^2.0.0",
+    "koa-override": "^3.0.0",
     "mime-types": "^2.1.17",
     "sendmessage": "^1.1.0",
     "urllib": "^2.25.1",
@@ -107,7 +106,10 @@
     "url": "https://github.com/eggjs/egg.git"
   },
   "engines": {
-    "node": ">= 6.0.0"
+    "node": ">= 8.0.0"
+  },
+  "publishConfig": {
+    "tag": "next"
   },
   "license": "MIT"
 }