<select id="input_select" type="number" >
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
</select>
//js
var _input =3;//从后台获取的值
$("#input_select option[value='"+_input +"']").attr('selected','selected');