JQuery+Ajax制作省市联动

 $(document).ready(function () {
             $("#Province").append("<option value=''>" + "--请选择--" + "</option>");
             $("#City").append("<option value=''>" + "--请选择--" + "</option>");
             $("#District").append("<option value=''>" + "--请选择--" + "</option>");
             $.ajax({
                 url: "Handler1.ashx?type=0", //路径 地址
                 type: "get", //类型，post\get
                 dataType: "json", //json数据
                 success: function (msg) {//返回结果
                     for (var i = ; i < msg.length; i++) {
                         $("#Province").append("<option value='" + msg[i].ProvinceID + "'>" + msg[i].ProvinceName + "</option>");
                     }
                 }
             });
             //市
             $("#Province").change(function () {
                 $("#City").empty(); //清空数据
                 $("#District").empty(); //清空数据
                 $("#District").append("<option value=''>" + "--请选择--" + "</option>");
                 var ProvinceID = $(this).val();

                 $.ajax({
                     url: "Handler1.ashx?type=1",
                     type: "get", //类型
                     data: {
                         ProvinceID: ProvinceID
                     },
                     dataType: "json", //json数据
                     success: function (msg) {
                         for (var i = ; i < msg.length; i++) { $("#City").append("<option value='" + msg[i].CityID + "'>" + msg[i].CityName + "</option>"); }
                     }
                 });
             });

             //区
             $("#City").change(function () {
                 $("#District").empty(); //清空数据
                 var CityID = $(this).val();
                 $.ajax({
                     url: "Handler1.ashx?type=2",
                     type: "get", //类型
                     data: {
                         CityID: CityID
                     },
                     dataType: "json", //json数据
                     success: function (msg) {
                         for (var i = ; i < msg.length; i++) { $("#District").append("<option value='" + msg[i].DistrictID + "'>" + msg[i].DistrictName + "</option>"); }
                     }
                 });

             });
         });

 <select id="Province"></select>
 <select id="City"></select>
 <select id="District" ></select>
         

结合ajax（一般处理程序）

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Web;
 using System.Data;
 using System.Web.Script.Serialization;

 namespace GovSystem.Company
 {
     /// <summary>
     /// Handler1 的摘要说明
     /// </summary>
     public class Handler1 : IHttpHandler
     {

         public string text;
         public void ProcessRequest(HttpContext context)
         {
             int action = Convert.ToInt32(context.Request.QueryString["type"]);
             switch (action)
             {
                 case (int)GetType.省:
                     text = Sel_Province(context);
                     break;
                 case (int) GetType.市:
                     text=Sel_City(context);
                     break;
                 case (int)GetType.区:
                     text = Sel_District(context);
                     break;
             }
             context.Response.ContentType = "text/plain";
             context.Response.Write(text);
         }
         //省
         private string Sel_Province(HttpContext context)
         {
             XieKe.BLL.S_Province b_Province = new XieKe.BLL.S_Province();
             DataTable dt=b_Province.GetList("").Tables[];
             List<XieKe.Model.S_Province> listInfo = new List<XieKe.Model.S_Province>();
             for (int i = ; i < dt.Rows.Count; i++)
             {
                 XieKe.Model.S_Province m_Province = new XieKe.Model.S_Province { ProvinceID = long.Parse(dt.Rows[i]["ProvinceID"].ToString()), DateCreated = Convert.ToDateTime(dt.Rows[i]["DateCreated"]), DateUpdated = Convert.ToDateTime(dt.Rows[i]["DateUpdated"]), ProvinceName = dt.Rows[i]["ProvinceName"].ToString() };
                 listInfo.Add(m_Province);
             }
             JavaScriptSerializer jssp = new JavaScriptSerializer();
             string s= jssp.Serialize(listInfo);
             return s;
         }
         //市
         private string Sel_City(HttpContext context)
         {
             string ProvinceID = context.Request.QueryString["ProvinceID"];
             XieKe.BLL.S_City b_City = new XieKe.BLL.S_City();

             DataTable dt = b_City.GetList("ProvinceID="+ProvinceID).Tables[];
             List<XieKe.Model.S_City> listInfo = new List<XieKe.Model.S_City>();
             for (int i = ; i < dt.Rows.Count; i++)
             {
                 XieKe.Model.S_City m_City = new XieKe.Model.S_City { CityID = long.Parse(dt.Rows[i]["CityID"].ToString()), CityName = dt.Rows[i]["CityName"].ToString(), DateCreated = Convert.ToDateTime(dt.Rows[i]["DateCreated"]), DateUpdated = Convert.ToDateTime(dt.Rows[i]["DateUpdated"]), ProvinceID = long.Parse(dt.Rows[i]["ProvinceID"].ToString()), ZipCode = dt.Rows[i]["ZipCode"].ToString() };
                 listInfo.Add(m_City);
             }
             JavaScriptSerializer jssp = new JavaScriptSerializer();
             return jssp.Serialize(listInfo);
         }
         //区
         private string Sel_District(HttpContext context)
         {
             string CityID = context.Request.QueryString["CityID"];
             XieKe.BLL.S_District b_City = new XieKe.BLL.S_District();
             DataTable dt = b_City.GetList("CityID=" + CityID).Tables[];
             List<XieKe.Model.S_District> listInfo = new List<XieKe.Model.S_District>();
             for (int i = ; i < dt.Rows.Count; i++)
             {
                 XieKe.Model.S_District m_District = new XieKe.Model.S_District { CityID = Convert.ToInt32(dt.Rows[i]["CityID"]), DistrictName = dt.Rows[i]["DistrictName"].ToString() };
                 listInfo.Add(m_District);
             }
             JavaScriptSerializer jssp = new JavaScriptSerializer();
             return jssp.Serialize(listInfo);
         }
         public bool IsReusable
         {
             get
             {
                 return false;
             }
         }
         public enum GetType
         {
             省 = ,
             市 = ,
             区 = ,
         };
     }

 }