SOURCE

new Vue({
    el: '#app',
    data() {
    return {
         defaultValue: '',
        }
    },
    created() {
      this.getValue()
    },
    methods: {
        getValue() {
            setTimeout(() => {
                this.defaultValue = 'yiminghe'
            },1000)
        }
    }
})

<div id="app">
	<div>
		<a-select v-model="defaultValue" style="width: 120px">
			<a-select-option value="jack">
				Jack
			</a-select-option>
			<a-select-option value="lucy">
				Lucy
			</a-select-option>
			<a-select-option value="disabled" disabled>
				Disabled
			</a-select-option>
			<a-select-option value="Yiminghe">
				yiminghe
			</a-select-option>
		</a-select>
	</div>
</div>