<div id="slct">
  <select  v-model="slct">
    <option>A</option>
    <option>B</option>
    <option>C</option>
  </select>
  <span>Selected: {{ slct }}</span>
</div>

new Vue({
  el : '#slct',
  data : {
    slct : '1',
  },
  mounted : function(){
    var that = this;
    setTimeout(function(){
      that.slct = '11';
    },1000);
  },
});