<el-menu :default-active="active" ref="menu">
      <el-menu-item
        :index="item.id"
        v-for="item in currentList"
        :key="item.id"
        @click="menuSelect(item)"
      >
        <span slot="title">{{ item.templateName }}</span>
      </el-menu-item>
    </el-menu>

	// 试试如下设置
    (this.$refs.menu as any).activeIndex = "";