先来看看效果:
 
 Html源码:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">  
<html xmlns="http://www.w3.org/1999/xhtml">  
<head>  
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />  
<title>动态改变菜单</title>  
<script type="text/javascript" src="jquery.js"></script>  
<script type="text/javascript" src="SelectMenu.js"></script>  
</head>  
<body>  
<form action="#">  
<br/>  
<br/>  
<br/>  
    <div class="Address">  
        <span class="Province">Province:  
            <select>  
                <option value="" selected="selected">Please Choose Province</option>  
                <option value="HeBei">HeBei</option>  
                <option value="ShanDong">ShanDong</option>  
            </select>   
        </span>  
        <span class="City" style="display:none">City:  
            <select>  
            </select>  
        </span>  
        <span class="Area" style="display:none">Area:  
            <select>  
            </select>  
        </span>  
        <br/>  
         <br/>  
        <span class="AddressSelect" style="display:none">  
        </span>  
    </div>  
</form>  
</body>  
</html>  
Javascript源码 
$(document).ready(function () {  
    //找到三个下拉框   
    var ProvinceSelect = $(".Province").children("select");  
    var CitySelect = $(".City").children("select");  
    var AreaSelect = $(".Area").children("select");  
    var AddressSelect=$(".AddressSelect");  
    //给第二个下拉框注册事件   
    ProvinceSelect.change(function () {  
        //1、获取当前下拉框的值   
         var ProvinceValue = $(this).val();  
        //1.1只要第一个下拉框内容有变化,第三个下拉框就要隐藏起来   
        AreaSelect.parent().hide();  
        AddressSelect.hide();  
        AddressSelect.html("");  
        //2、如果值不为空,则显示城市下拉框   
         if (ProvinceValue != "") {  
                   CitySelect.html("");  
                   $("<option value=''>Please Choose City</option>").appendTo(CitySelect);  
                    switch(ProvinceValue)  
                       {  
                        //实际项目中,这个城市数组肯定是在服务器获取的,这里为了简便,我就直接自定义了一个数组   
                        //如果追求完美,这里还可以加一道缓存,防止重复获取   
                       case "HeBei":  
                            var CityOfHeBei=["ShiJiaZhuang","CangZhou","LangFang"];   
                            for(var i=0;i<CityOfHeBei.length;i++){  
                                $("<option value='"+CityOfHeBei[i]+"'>"+CityOfHeBei[i]+"</option>").appendTo(CitySelect);  
                            }  
                             break;  
                       case "ShanDong":  
                            var CityOfShanDon=["JiNan","DeZhou","QingDao"];       
                            for(var i=0;i<CityOfShanDon.length;i++){  
                                $("<option value='"+CityOfShanDon[i]+"'>"+CityOfShanDon[i]+"</option>").appendTo(CitySelect);  
                            }  
                            break;  
                       }  
                 CitySelect.parent().show();     
        } else {  
            CitySelect.parent().hide();  
        }  
    });  
    //给第二个下拉框注册事件   
     CitySelect.change(function () {  
            var CityValue = $(this).val();        
            AddressSelect.hide();  
            AreaSelect.parent().hide();   
            AddressSelect.html("");  
             if (CityValue != "") {  
                   AreaSelect.html("");  
                   $("<option value=''>Please Choose Area</option>").appendTo(AreaSelect);  
                    switch(CityValue)  
                       {  
                       //实际项目中,这个区数组肯定是在服务器获取的,这里为了简便,我就直接自定义了一个数组   
                       //如果追求完美,这里还可以加一道缓存,防止重复获取   
                       case "ShiJiaZhuang":  
                            var AreaOfCity=["GaoXinQu","KaiFaQu","XinHuaQu"];     
                            for(var i=0;i<AreaOfCity.length;i++){  
                                $("<option value='"+AreaOfCity[i]+"'>"+AreaOfCity[i]+"</option>").appendTo(AreaSelect);  
                            }  
                             break;  
                       case "CangZhou":  
                            var AreaOfCity=["XinHuaQu","YunHeQu"];        
                            for(var i=0;i<AreaOfCity.length;i++){  
                                $("<option value='"+AreaOfCity[i]+"'>"+AreaOfCity[i]+"</option>").appendTo(AreaSelect);  
                            }  
                            break;  
                       case "LangFang":  
                            var AreaOfCity=["AnCiQu","GuangYangQu"];  
                            for(var i=0;i<AreaOfCity.length;i++){  
                                $("<option value='"+AreaOfCity[i]+"'>"+AreaOfCity[i]+"</option>").appendTo(AreaSelect);  
                            }  
                            break;  
                       case "QingDao":  
                            var AreaOfCity=["GaoXinQu","KaiFaQu","XinHuaQu"];     
                            for(var i=0;i<AreaOfCity.length;i++){  
                                $("<option value='"+AreaOfCity[i]+"'>"+AreaOfCity[i]+"</option>").appendTo(AreaSelect);  
                            }  
                             break;  
                       case "DeZhou":  
                            var AreaOfCity=["XinHuaQu","YunHeQu"];        
                            for(var i=0;i<AreaOfCity.length;i++){  
                                $("<option value='"+AreaOfCity[i]+"'>"+AreaOfCity[i]+"</option>").appendTo(AreaSelect);  
                            }  
                            break;  
                       case "JiNan":  
                            var AreaOfCity=["AnCiQu","GuangYangQu"];  
                            for(var i=0;i<AreaOfCity.length;i++){  
                                $("<option value='"+AreaOfCity[i]+"'>"+AreaOfCity[i]+"</option>").appendTo(AreaSelect);  
                            }  
                            break;  
                       }  
                     AreaSelect.parent().show();   
             } else {  
                     AreaSelect.parent().hide();  
            }  
    });  
    AreaSelect.change(function(){  
            var AreaValue=$(this).val();  
            AddressSelect.html("");  
            if (AreaValue!=""){  
                $("<span>The Address Is --Province: "+ProvinceSelect.val()+"  City: "+CitySelect.val()+"  Area: "+AreaSelect.val()+"</span>").appendTo(AddressSelect);  
            AddressSelect.show();  
            //alert("The Address Is  Province: "+ProvinceSelect.val()+"  City: "+CitySelect.val()+"  Area: "+AreaSelect.val());   
                }                    
     })  
});  
这里还引用了Jquery,貌似实现这个效果,用不用都无所谓,最近为了熟悉Jquery的用法,所以就加上了。