diff --git a/.autod.conf b/.autod.conf
index d9af5a64..d87055e7 100644
--- a/.autod.conf
+++ b/.autod.conf
@@ -12,6 +12,7 @@ module.exports = {
     'mocha',
     'thunk-mocha',
     'intelli-espower-loader',
+    'power-assert',
   ],
   devdep: [
     'autod',
diff --git a/lib/debug_command.js b/lib/debug_command.js
index 98c9af35..7c7703cf 100644
--- a/lib/debug_command.js
+++ b/lib/debug_command.js
@@ -14,15 +14,7 @@ class DebugCommand extends Command {
   }
 
   * run(cwd, args) {
-    args.push('--baseDir');
-    args.push(cwd);
-    args.push('--cluster');
-    args.push('1');
-
-    const eggPath = this.getFrameworkOrEggPath(cwd);
-    if (eggPath) {
-      args.push(`--eggPath=${eggPath}`);
-    }
+    args = yield this.helper.formatArgs(cwd, args);
 
     const options = {
       env: Object.assign({}, process.env),
@@ -74,10 +66,6 @@ class DebugCommand extends Command {
   help() {
     return 'Debug mode start';
   }
-
-  getFrameworkOrEggPath(cwd) {
-    return this.utils.getFrameworkOrEggPath(cwd);
-  }
 }
 
 module.exports = DebugCommand;
diff --git a/lib/dev_command.js b/lib/dev_command.js
index 53865b27..342347b6 100644
--- a/lib/dev_command.js
+++ b/lib/dev_command.js
@@ -7,19 +7,10 @@ class DevCommand extends Command {
   * run(cwd, args) {
     const execArgv = args ? args.filter(str => str.indexOf('--debug') === 0 || str.indexOf('--inspect') === 0) : [];
 
-    args.push('--baseDir');
-    args.push(cwd);
-    args.push('--cluster');
-    args.push('1');
-
-    const eggPath = this.getFrameworkOrEggPath(cwd);
-
-    if (eggPath) {
-      args.push(`--eggPath=${eggPath}`);
-    }
+    args = yield this.helper.formatArgs(cwd, args);
 
     const options = {
-      env: process.env,
+      env: Object.assign({}, process.env),
       execArgv,
     };
 
@@ -33,10 +24,6 @@ class DevCommand extends Command {
   help() {
     return 'local env start';
   }
-
-  getFrameworkOrEggPath(cwd) {
-    return this.utils.getFrameworkOrEggPath(cwd);
-  }
 }
 
 module.exports = DevCommand;
diff --git a/lib/helper.js b/lib/helper.js
index cc185658..67483796 100644
--- a/lib/helper.js
+++ b/lib/helper.js
@@ -2,7 +2,10 @@
 
 const path = require('path');
 const glob = require('glob');
+const detect = require('detect-port');
+const utils = require('egg-utils');
 
+exports.defaultPort = 7001;
 exports.serverBin = path.join(__dirname, 'start-cluster');
 
 exports.getTestFiles = function() {
@@ -20,3 +23,26 @@ exports.getTestFiles = function() {
 exports.checkDeps = function* () {
   return true;
 };
+
+exports.formatArgs = function* (cwd, args) {
+  args.push('--baseDir');
+  args.push(cwd);
+  args.push('--cluster');
+  args.push('1');
+
+  const eggPath = utils.getFrameworkOrEggPath(cwd);
+  if (eggPath) {
+    args.push(`--eggPath=${eggPath}`);
+  }
+
+  // auto detect available port
+  if (args.indexOf('-p') === -1 && args.indexOf('--port') === -1) {
+    const port = yield detect(exports.defaultPort);
+    if (port !== exports.defaultPort) {
+      args.push('-p', port);
+      console.warn(`[egg-bin] server port ${exports.defaultPort} is in use, now using port ${port}\n`);
+    }
+  }
+  return args;
+};
+
diff --git a/package.json b/package.json
index b9beee7f..b139a3f4 100644
--- a/package.json
+++ b/package.json
@@ -11,7 +11,8 @@
     "childprocess": "^2.0.2",
     "commander": "^2.9.0",
     "common-bin": "^1.0.0",
-    "debug": "^2.3.3",
+    "debug": "^2.4.4",
+    "detect-port": "^1.0.7",
     "egg-utils": "^1.0.0",
     "glob": "^7.1.1",
     "intelli-espower-loader": "^1.0.1",
@@ -27,7 +28,7 @@
     "autod": "^2.7.1",
     "coffee": "^3.3.0",
     "egg-ci": "^1.1.0",
-    "eslint": "^3.12.1",
+    "eslint": "^3.12.2",
     "eslint-config-egg": "^3.2.0",
     "mm": "^2.0.0"
   },
diff --git a/test/egg-cov.test.js b/test/egg-cov.test.js
index e987d8e5..4dc1cc3c 100644
--- a/test/egg-cov.test.js
+++ b/test/egg-cov.test.js
@@ -63,9 +63,7 @@ describe('egg-bin cov', () => {
 
   it('should fail when test fail', done => {
     mm(process.env, 'TESTS', 'test/fail.js');
-    coffee.fork(eggBin, [ 'cov' ], {
-      cwd: appdir,
-    })
+    coffee.fork(eggBin, [ 'cov' ], { cwd: appdir })
     .coverage(false)
     // .debug()
     .expect('stdout', /1\) should fail/)
@@ -76,9 +74,7 @@ describe('egg-bin cov', () => {
 
   it('should fail when test fail with power-assert', done => {
     mm(process.env, 'TESTS', 'test/power-assert-fail.js');
-    coffee.fork(eggBin, [ 'cov' ], {
-      cwd: appdir,
-    })
+    coffee.fork(eggBin, [ 'cov' ], { cwd: appdir })
     .coverage(false)
     // .debug()
     .expect('stdout', /1\) should fail/)
@@ -90,9 +86,7 @@ describe('egg-bin cov', () => {
 
   it('should warn when require intelli-espower-loader', done => {
     mm(process.env, 'TESTS', 'test/power-assert-fail.js');
-    coffee.fork(eggBin, [ 'cov', '-r', 'intelli-espower-loader' ], {
-      cwd: appdir,
-    })
+    coffee.fork(eggBin, [ 'cov', '-r', 'intelli-espower-loader' ], { cwd: appdir })
     .coverage(false)
     // .debug()
     .expect('stderr', /manually require `intelli-espower-loader`/)
diff --git a/test/egg-debug.test.js b/test/egg-debug.test.js
index e8fb3b8e..b59eb14a 100644
--- a/test/egg-debug.test.js
+++ b/test/egg-debug.test.js
@@ -4,6 +4,7 @@ const path = require('path');
 const coffee = require('coffee');
 const mm = require('mm');
 const rimraf = require('rimraf');
+const net = require('net');
 
 describe('egg-bin debug', () => {
   const eggBin = require.resolve('../bin/egg-bin.js');
@@ -16,22 +17,37 @@ describe('egg-bin debug', () => {
   afterEach(mm.restore);
 
   it('should startCluster success', done => {
-    coffee.fork(eggBin, [ 'debug' ], {
-      cwd: appdir,
-    })
-    .debug()
+    coffee.fork(eggBin, [ 'debug' ], { cwd: appdir })
+    // .debug()
     .expect('stdout', /,"workers":1}/)
     .expect('code', 0)
     .end(done);
   });
 
   it('should startCluster with port', done => {
-    coffee.fork(eggBin, [ 'debug', '--port', '6001' ], {
-      cwd: appdir,
-    })
-    .debug()
+    coffee.fork(eggBin, [ 'debug', '--port', '6001' ], { cwd: appdir })
+    // .debug()
     .expect('stdout', `{"baseDir":"${appdir}","workers":1,"port":"6001"}\n`)
     .expect('code', 0)
     .end(done);
   });
+
+  describe('auto detect available port', () => {
+    let server;
+    before(done => {
+      server = net.createServer();
+      server.listen(7001, done);
+    });
+
+    after(() => server.close());
+
+    it('should auto detect available port', done => {
+      coffee.fork(eggBin, [ 'debug' ], { cwd: appdir })
+      // .debug()
+      .expect('stdout', /,"workers":1}/)
+      .expect('stderr', /\[egg-bin] server port 7001 is in use/)
+      .expect('code', 0)
+      .end(done);
+    });
+  });
 });
diff --git a/test/egg-dev.test.js b/test/egg-dev.test.js
index 47173435..71e196f0 100644
--- a/test/egg-dev.test.js
+++ b/test/egg-dev.test.js
@@ -2,15 +2,14 @@
 
 const path = require('path');
 const coffee = require('coffee');
+const net = require('net');
 
 describe('egg-bin dev', () => {
   const eggBin = require.resolve('../bin/egg-bin.js');
   const appdir = path.join(__dirname, 'fixtures/demo-app');
 
   it('should startCluster success', done => {
-    coffee.fork(eggBin, [ 'dev' ], {
-      cwd: appdir,
-    })
+    coffee.fork(eggBin, [ 'dev' ], { cwd: appdir })
     // .debug()
     .expect('stdout', `{"baseDir":"${appdir}","workers":1}\n`)
     .expect('code', 0)
@@ -18,19 +17,34 @@ describe('egg-bin dev', () => {
   });
 
   it('should startCluster with port', done => {
-    coffee.fork(eggBin, [ 'dev', '--port', '6001' ], {
-      cwd: appdir,
-    })
+    coffee.fork(eggBin, [ 'dev', '--port', '6001' ], { cwd: appdir })
     // .debug()
     .expect('stdout', `{"baseDir":"${appdir}","workers":1,"port":"6001"}\n`)
     .expect('code', 0)
     .end(done);
   });
 
+  describe('auto detect available port', () => {
+    let server;
+    before(done => {
+      server = net.createServer();
+      server.listen(7001, done);
+    });
+
+    after(() => server.close());
+
+    it('should auto detect available port', done => {
+      coffee.fork(eggBin, [ 'dev' ], { cwd: appdir })
+      // .debug()
+      .expect('stdout', `{"baseDir":"${appdir}","workers":1}\n`)
+      .expect('stderr', /\[egg-bin] server port 7001 is in use/)
+      .expect('code', 0)
+      .end(done);
+    });
+  });
+
   it.skip('should startCluster with execArgv --debug', done => {
-    coffee.fork(eggBin, [ 'dev', '--debug=7000' ], {
-      cwd: appdir,
-    })
+    coffee.fork(eggBin, [ 'dev', '--debug=7000' ], { cwd: appdir })
     // .debug()
     .expect('stdout', `{"baseDir":"${appdir}","workers":1}\n`)
     .expect('stderr', /Debugger listening on .*7000/)
@@ -39,9 +53,7 @@ describe('egg-bin dev', () => {
   });
 
   it.skip('should startCluster with execArgv --inspect', done => {
-    coffee.fork(eggBin, [ 'dev', '--inspect=7000' ], {
-      cwd: appdir,
-    })
+    coffee.fork(eggBin, [ 'dev', '--inspect=7000' ], { cwd: appdir })
     // .debug()
     .expect('stdout', `{"baseDir":"${appdir}","workers":1}\n`)
     .expect('stderr', /Debugger listening on .*7000/)