<div class="layui-form-item">
 <label class="layui-form-label">城市</label>
 <div class="layui-input-inline">
  <select name="city" lay-filter="province">
   <option value=""></option>
   <option value="11">北京市</option>
   <option value="12">天津市</option>
   <option value="13">河北省</option>
   <option value="14">山西省</option>
   <option value="15">内蒙古自治区</option>
   <option value="21">辽宁省</option>
   <option value="22">吉林省</option>
   <option value="23">黑龙江省</option>
   <option value="31">上海市</option>
   <option value="32">江苏省</option>
   <option value="33">浙江省</option>
   <option value="34">安徽省</option>
   <option value="35">福建省</option>
   <option value="36">江西省</option>
   <option value="37">山东省</option>
   <option value="41">河南省</option>
   <option value="42">湖北省</option>
   <option value="43">湖南省</option>
   <option value="44">广东省</option>
   <option value="45">广西壮族自治区</option>
   <option value="46">海南省</option>
   <option value="50">重庆市</option>
   <option value="51">四川省</option>
   <option value="52">贵州省</option>
   <option value="53">云南省</option>
   <option value="54">西藏自治区</option>
   <option value="61">陕西省</option>
   <option value="62">甘肃省</option>
   <option value="63">青海省</option>
   <option value="64">宁夏回族自治区</option>
   <option value="65">新疆维吾尔自治区</option>
   <option value="71">台湾省</option>
   <option value="81">香港特别行政区</option>
   <option value="82">澳门特别行政区</option>
  </select>
 </div>
 <div class="layui-input-inline">
  <select name="city" id="city">
   <option value=""></option>
  </select>
 </div>
</div>

form.on('select(province)', function(data){
   $.getJSON("/api/getCity?pid="+data.value, function(data){
    var optionstring = "";
    $.each(data.data, function(i,item){
     optionstring += "<option value=\"" + item.code + "\" >" + item.name + "</option>";
    });
    $("#city").html('<option value=""></option>' + optionstring);
    form.render('select'); //这个很重要
   });
});

{
 "status": 200,
 "message": "result",
 "data": [
  {
   "code": "3418",
   "name": "宣城市",
   "province": "34"
  },
  {
   "code": "3417",
   "name": "池州市",
   "province": "34"
  },
  {
   "code": "3416",
   "name": "亳州市",
   "province": "34"
  },
  {
   "code": "3415",
   "name": "六安市",
   "province": "34"
  },
  {
   "code": "3413",
   "name": "宿州市",
   "province": "34"
  },
  {
   "code": "3412",
   "name": "阜阳市",
   "province": "34"
  },
  {
   "code": "3411",
   "name": "滁州市",
   "province": "34"
  },
  {
   "code": "3408",
   "name": "安庆市",
   "province": "34"
  },
  {
   "code": "3407",
   "name": "铜陵市",
   "province": "34"
  },
  {
   "code": "3406",
   "name": "淮北市",
   "province": "34"
  },
  {
   "code": "3405",
   "name": "马鞍山市",
   "province": "34"
  },
  {
   "code": "3404",
   "name": "淮南市",
   "province": "34"
  },
  {
   "code": "3403",
   "name": "蚌埠市",
   "province": "34"
  },
  {
   "code": "3402",
   "name": "芜湖市",
   "province": "34"
  },
  {
   "code": "3401",
   "name": "合肥市",
   "province": "34"
  }
 ]
}