废话不说，上代码！

<a-menu theme="dark" mode="inline" :selectedKeys="[$route.path]">
          <a-menu-item :key="'/home'">
            <router-link to="home">
              <a-icon type="user" />
              <span>nav 1</span>
            </router-link>
          </a-menu-item>
          <a-menu-item :key="'/about'">
            <router-link to="about">
              <a-icon type="video-camera" />
              <span>nav 2</span>
            </router-link>
          </a-menu-item>
          <a-menu-item :key="'/123123'">
            <router-link to="123123">
              <a-icon type="upload" />
              <span>nav 3</span>
            </router-link>
          </a-menu-item>
        </a-menu>

重点：

1，selectedkeys要设置成$route.path地址

2，a-menu-item 的key设置成要去的地址

刷新页面，成功！