//省市縣數據格式var province_city_county_data=[  {    province:"四川",    city:[      {        cityName:"成都",        county:["成都市","崇州市","金堂縣"]      },      {        cityName:"南充",        county:["儀隴縣","南部縣","營山縣"]      }    ]  },  {    province:"北京",    city:[      {  cityName:"北京市",        county:["東城區","朝陽區"]      }    ]  },  {    province:"安徽",    city:[      {  cityName:"安慶",        county:["安慶市","懷寧縣","潛山縣"]      },      {  cityName:"蚌埠",        county:["蚌埠市","固鎮縣","懷遠縣"]      }    ]  }]var opt0 = ["省份","地級市","市、縣級市、縣"];var selectID_arr2=["provinceid","cityid","countyid"];var province_index;window.onload = function(){  //初始化下拉框  function init_select(){    init_title();    init_province();    bind_province();  }  //初始化提示標題  function init_title(){    for(var k = 0;k<selectID_arr2.length;k++){      var select_obj= document.getElementById(selectID_arr2[k]);      select_obj.options[0]=new Option(opt0[k],opt0[k]);    }  }  //初始化省份  function init_province(){    var province_select_obj = document.getElementById(selectID_arr2[0]);    var province_len = province_city_county_data.length;    for(var i = 0;i<province_len;i++){      province_select_obj.options[i+1] = new Option(province_city_county_data[i].province,province_city_county_data[i].province);    }  }  //給省份綁定onchange事件  function bind_province(){    var province_select_obj = document.getElementById(selectID_arr2[0]);    province_select_obj.onchange=function(){      var opt_index =province_select_obj.selectedIndex;      if(opt_index!=0){        province_index = opt_index-1;  //每個省份的序號比 option 的下標要小1        init_city(province_index);        bind_city();        init_county(province_index,0);      }else{        clear_city();        clear_county();      }    }  }  //選擇一個省份才能初始化地級市  function init_city(index){    clear_city();    var city_len = province_city_county_data[index].city.length;    for(var i = 0;i<city_len;i++){      document.getElementById(selectID_arr2[1]).options[i+1] = new Option(province_city_county_data[index].city[i].cityName,province_city_county_data[index].city[i].cityName);    }    document.getElementById(selectID_arr2[1]).options[1].selected = true;  }  //清除地級市信息  function clear_city(){    var city_select_obj = document.getElementById(selectID_arr2[1]);    city_select_obj.options.length=0; //每次選中一個新的省份 都重新刪除地級市的信息    init_title();   //重新初始化標題  }  //給地級市綁定onchange事件  function bind_city(){    var city_select_obj = document.getElementById(selectID_arr2[1]);    city_select_obj.onchange=function(){      var opt_index =city_select_obj.selectedIndex;      if(opt_index!=0){        init_county(province_index,opt_index-1);      }else{        clear_county();      }    }  }  //選擇一個地級市后才能初始化縣  function init_county(index,city_index){    clear_county();    var county_len = province_city_county_data[index].city[city_index].county.length;    for(var i = 0;i<county_len;i++){      document.getElementById(selectID_arr2[2]).options[i+1] = new Option(province_city_county_data[index].city[city_index].county[i],province_city_county_data[index].city[city_index].county[i]);    }    document.getElementById(selectID_arr2[2]).options[1].selected = true;  }  //清除縣城信息  function clear_county(){    var county_select_obj = document.getElementById(selectID_arr2[2]);    county_select_obj.options.length=0; //每次選中一個新的地級市 都重新刪除縣的信息    init_title();   //重新初始化標題  }  init_select()}

<select id="provinceid"></select><select id="cityid"></select><select id="countyid"></select>