代码：

<template>
  <div>
<div class="block">
  <span class="demonstration">默认 click 触发子菜单</span>
  <el-cascader
    v-model="value"
    :options="options"
    @change="handleChange"></el-cascader>
</div>
<div class="block">
  <span class="demonstration">hover 触发子菜单</span>
  <el-cascader
    v-model="value"
    :options="options"
    :props="{ expandTrigger: 'hover' }"
    @change="handleChange"></el-cascader>
</div>
</div>
</template>


<script>
  export default {
    data() {
      return {
        options: [],
        father:[{id:1,pid:'0',name:'安徽省',code:'340000',level:1},{id:13,pid:'0',name:'河北省',code:'350000',level:1}],
        children :[{code: "340800",id: 139,name:"安庆市",Level: 2,pid: "340000"},{code: "340300",id: 134,name:"蚌埠市",pid:"340000",level: 2},{code: "340301",id: 134,name:"唐山市",pid:"350000",level: 2}],
        grandChild:[{code: "340800",id: 139,name:"安庆市",Level: 3,pid: "340800"},{code: "340300",id: 139,name:"蚌埠市",Level: 3,pid: "340300"},{code: "340301",id: 139,name:"路北区",Level: 3,pid: "340301"}]
      };
    },
    mounted(){
      let data = [];
  this.father.forEach(fatherObj => {
  let fatherOption = {
    value: fatherObj.name,
    label: fatherObj.name,
    children: []
  };

  this.children.forEach(childObj => {
    if (fatherObj.code === childObj.pid) {
      let childOption = {
        value: childObj.name,
        label: childObj.name,
        children: []
      };

    this.grandChild.forEach(grandChildObj => {
        if (childObj.code === grandChildObj.pid) {
          let grandChildOption = {
            value: grandChildObj.name,
            label: grandChildObj.name
          };

          childOption.children.push(grandChildOption);
        }
      });

      fatherOption.children.push(childOption);
    }
  });

  data.push(fatherOption);
  this.options=data
});
    },
    methods: {
      handleChange(value) {
        console.log(value);
      }
    },
  
  };
</script>