代码

<template>
  <div class="app">
    <el-form ref="form" :model="form">
      <el-form-item label="手机品牌">
        <el-select v-model="form.phoneBrand" placeholder="请选择" @change="changeSelect">
          <el-option
            v-for="(item,index) in brandOptions"
            :key="index"
            :label="item"
            :value="item"
          />
        </el-select>

      </el-form-item>
      <el-form-item label="手机型号">
        <el-select v-model="form.phoneType" placeholder="请选择">
          <el-option
            v-for="(item,index) in typeOptions"
            :key="index"
            :label="item"
            :value="item"
          />
        </el-select>
      </el-form-item>
    </el-form>
  </div>
</template>
<script>
export default {
  data() {
    return {
      brandOptions: ['OPPO', '华为', 'VIVO'],
      brandObj: { 'OPPO': ['OPPO1', 'OPPO2', 'OPPO3'], '华为': ['华为1', '华为2', '华为3'], 'VIVO': ['VIVO1', 'VIVO2', 'VIVO3'] },
      typeOptions: [],
      form: {
        phoneBrand: '',
        phoneType: ''
      }
    }
  },
  methods: {
    changeSelect() {
      // 清空手机型号内容
      this.form.phoneType = ''

      // 遍历手机品牌的下拉选项数组
      for (const k in this.brandOptions) {
        // 手机品牌内容 是否等于 手机品牌的下拉选择数组中的某一项
        if (this.form.phoneBrand === this.brandOptions[k]) {
          this.typeOptions = this.brandObj[this.form.phoneBrand]
        }
      }
    }
  }
}
</script>
<style>
.app{
  margin:20px;
  width: 100%;
}
</style>