<div>
<div class="nav">
<div class="icon">132</div>
<el-menu :default-active="activeIndex === '' ? '/' : activeIndex" class="el-menu-demo" mode="horizontal" @select="handleSelect" router>
<el-menu-item index="/" icon="el-icon-search">1</el-menu-item>
<el-submenu index="2">
<template slot="title">2</template>
<el-menu-item index="2-1">2-1</el-menu-item>
</el-submenu>
<el-menu-item index="3">3</el-menu-item>
<el-menu-item index="4">4</el-menu-item>
</el-menu>
<div style="clear: both;"></div>
</div>
<div class="show">
<hello-world></hello-world>
</div>
</div>

要用嵌套路由。
请参考vue-router的官方例子,https://jsfiddle.net/yyx99080...