SOURCE

var Main = {
    data() {
      return {
        tableData: [
          {},
          {}
        ]
      };
    },
    methods: {
      test() {
        this.$refs.multipleTable.toggleRowSelection(this.tableData[1]);
      }
    }
  };
window.onload = function() {
  var Ctor = Vue.extend(Main)
	new Ctor().$mount('#app')
}

<div id="app">
  <span class="demonstration">默认2</span>
  <el-table ref="multipleTable" :data="tableData">
     <el-table-column
      type="selection"
      width="55">
    </el-table-column>
     <el-table-column label="表头A">
       <template slot-scope="{$index}">第{{$index}}行</template>
     </el-table-column>
  </el-table>
  <el-button @click="test">第二行切换选中状态</el-button>
</div>

@import url("//unpkg.com/element-ui@2.3.6/lib/theme-chalk/index.css");