好像别的同学没有我这个问题欸 已经引用了fs ，在这之前都没什么问题，代码如下：

/*wechat.js*/
'use strict'


var Promise = require('bluebird')
var fs = require('fs')
var request = Promise.promisify(require('request'))
var util = require('./util')
var prefix = 'https://api.weixin.qq.com/cgi-bin/'
var api = {
    access_token:prefix +'token?grant_type=client_credential',
    upload: prefix + 'media/upload?'
}


function Wechat(opts){
    var that = this;
    this.appID = opts.appID
    this.appSecret = opts.appSecret
    this.getAccessToken =opts.getAccessToken
    this.saveAccessToken =opts.saveAccessToken
    this.fetchAccessToken()
    
}
Wechat.prototype.fetchAccessToken = function(data){
    var that = this
    if(this.access_token && this.expires_in){
        if(this.isValidAccessToken(this)){
            return Promise.resolve(this)
        }
    }


    return this.getAccessToken()
        .then(function(data){
            try{
                data = JSON.parse(data)
            }
            catch(e){
                return that.updateAccessToken()
            }

            if(that.isValidAccessToken(data)){
                return Promise.resolve(data)
            }
            else{
                return that.updateAccessToken()

            }
        })
        .then(function(data){
            that.access_token = data.access_token
            that.expires_in = data.expires_in
            that.saveAccessToken(data)

            return Promise.resolve(data)

        })
}

Wechat.prototype.isValidAccessToken = function(data){

    if(!data||!data.access_token||!data.expires_in){
        return false;
    }
    var access_token = data.access_token
    var expires_in = data.expires_in
    var now = (new Date().getTime())
    if(now<expires_in){
        return true;
    }
    else{
        return false;
    }
}
Wechat.prototype.updateAccessToken = function(){
    var appID = this.appID;
    var appSecret = this.appSecret;
    var url = api.access_token+'&appid='+appID+'&secret='+appSecret
    return new Promise(function(resolve,reject){
        request({url: url,json:true}).then(function(response){
            var data = response.body;
            var now = (new Date().getTime())
            var expires_in = now +(data.expires_in - 20) * 1000
            data.expires_in =expires_in;
        
            resolve(data)
        })
    })
}
Wechat.prototype.uploadMaterial = function(type, filepath){
    var that = this;
    console.log(fs.creatReadStream)
    var form = {
        media: fs.creatReadStream(filepath)

    }
    return new Promise(function(resolve,reject){
            that.fetchAccessToken()
            .then(function(data){
                var url = api.upload+'access_token='+data.access_token+'&type='+type
                request({method:'POST',url: url,formData:form,json:true}).then(function(response){
                    var _data = response.body;
                    if(_data){
                        
                        resolve(_data)
                    }
                    else{
                        throw new Error('Upload material fails')
                    }
                })
                .catch(function(err){
                    reject(err)
                })
                
            })

    })
}


Wechat.prototype.reply = function(){
    var content = this.body
    var message = this.weixin

    var xml = util.tpl(content,message)

    this.status = 200
    this.type = "application/xml"
    this.body = xml
}

module.exports=Wechat

/*weixin.js*/
'use strict'

var config = require('./config')
var Wechat = require('./wechat/wechat')

var wechatApi = new Wechat(config.wechat)

exports.reply = function*(next){
    var message = this.weixin

    if(message.MsgType ==='event'){
        if(message.Event==='subscribe'){
            if(message.EventKey){
                console.log('扫一扫进来的'+message.EventKey+'  '+message.Ticket)
            }
            this.body = '哈哈，你订阅了\r\n'
        }
        else if(message.Event==='unsubscribe'){
            console.log('取消关注了')
            this.body =''
        }
        else if(message.Event==='LOCATION'){
            this.body = '上报的位置是'+message.Latitude+'/'+message.Longitude+'-'+message.Precision
        }
        else if(message.Event==='CLICK'){
            this.body = '点击了菜单: '+message.EventKey
        }    
        else if(message.Event==='SCAN'){
            console.log('关注后扫二维码'+message.EventKey+'  '+message.Ticket)
            this.body = '看到你扫一下哦'
        }
        else if(message.Event==='VIEW'){
            this.body = '您点击了菜单中的连接 '+message.EventKey
        }    

    }
    else if(message.MsgType==='text'){
        var content = message.Content
        var reply = '你说的'+ content+' 让我有点懵比'

        if(content==='1'){
            reply = '星期一推荐《突然好想你》'

        }else if(content==='2'){
            reply = '星期二推荐《兄弟》'
        }else if(content === '3'){
            reply = '星期三推荐《如果我们不曾相遇》'
        }else if(content === '4'){
            reply = [{
                title:'技术改变世界',
                description:"你可以的",
                picUrl:'./22.jpg',
                url:'www.baidu.com'
            },{
                title:'node.js开发的',
                description:"你可以的",
                picUrl:'./22.jpg',
                url:'www.baidu.com'

            }]
        }else if(content === '5'){
            var data = yield wechatApi.uploadMaterial('image',__dirname+'./22.jpg')
            reply = {
                type:'image',
                mediaId:data.media_id
            }
        }
        this.body = reply

    }
    yield next
}