<select id="select" style="width : 80px;height : 30px;">
  //下拉框数据动态加载
</select>

$.ajax({ 
   url: "",  //后台webservice里的方法名称 
  contentType: "application/json; charset=utf-8",  
  type: "get", 
  async : true ,
  dataType: "json", 
  success: function (date) { 
    var optionstring = "";
    for (var j = 0; j < date.length;j++) {       
    optionstring += "<option value=\"" + date[j].id + "\" >" +"睡眠次数："+date[j].limitnumber+"&nbsp;&nbsp;睡眠时间："+date[j].sleeptime + "</option>"; 
    $("#select").html("<option value='0'>请选择...</option> "+optionstring);
          } 
        }, 
        error: function (msg) { 
          alert("出错了！"); 
        } 
      });