<el-checkbox v-model="checkAll" @change="handleCheckAllChange">全选</el-checkbox>

 <el-checkbox v-for="(city,i) in cities" :label="city.uuid" :key="i" v-model="city.relation"

    @change="handleCheckedCitiesChange">{{city.customerName}}</el-checkbox>

 <span slot="footer" class="dialog-footer">

    <el-button type="primary" :disabled="disabled" @click="classifyConfirm">确定</el-button>

    <el-button type="primary" @click="calceConfirn">取消</el-button>

 </span>

  data: function () {

     return {         checkAll: false,

         cities: [], //数据源
 5　　　}
 6　}
　　　　　　

 handleCheckAllChange(val) {

    if (this.checkAll) {

        this.cities.forEach(item => {

             item.relation = true   //只改变数据的状态

          })

      } else {

       this.cities.forEach(item => {

           item.relation = false

             })

           }

       },

 handleCheckedCitiesChange() {

   console.log(this.checkedCities);

   if (this.checkedCities.length == this.cities.length) {

   this.checkAll = true

     } else {

       this.checkAll = false

    }

 },

 //确认

             classifyConfirm() {

                 var checkedAll = [];

                 this.cities.forEach(item => {

                     if(item.relation == true){

                         checkedAll.push(item.uuid)   //确认的时候取状态为true的值，并把要用的字段取出来

                     }

                 })

                 // var checkedAll = [...new Set(this.checkedCities)] //数组去重

                 var that = this;

                 var data = {

                     "customerUuid":that.customerUuid,

                     "projectCustomerUuid":checkedAll.join(',')

                 };

                 console.log(checkedAll)

                 this.classLoading = true;

                 $.ajax({

                     url: Domain + '/xxxxx',

                     dataType: "json",

                     method: "POST",

                     // contentType: "application/json; charset=utf-8",

                     data:data,

                     success: function (ret) {

                         if (ret.retStatus == "1") {

                             that.$message({

                                 type: 'success',

                                 message: '保存成功!'

                             });

                             that.classLoading = false;                         }

                     }

                 })

             },

最开始在改变状态的时候就想着取id了，导致后面一系列的问题，后面经过大佬的提醒，在最开始的时候不要取值，只改变状态就行，最后提交的时候遍历数组,然后把每一项里面为true的取出来就可以了，很简单就解决了

或者html 这样写也可以：

<el-checkbox :indeterminate="roleIsIndeterminate" v-model="roleCheckAll" @change="handleRoleAllChange" :disabled="isAllChecked || onlyAllDisabled">全选</el-checkbox>
<el-checkbox-group v-model="checkedRoles" @change="handleCheckedRolesChange">
<el-checkbox v-for="role in roleList" :label="role.id" :key="role.id" :disabled="role.disabled">{{role.name}}</el-checkbox>
</el-checkbox-group>