改进了网上其他导航的缺点，比如多次鼠标滑过后动画会重复播放多次。本例使用了stop()函数，使鼠标移出之后动画自动停止，而且不会出现重复动画现象

代码如下：nav.js

$(document).ready(function(){
    $("ul.nav li a").parent().hover(function(){
            $(this).find("ul.nav_child").stop(false, true).slideDown('slow').show();
        }, function(){   
            $(this).find("ul.nav_child").stop(false, true).slideUp('slow');
    });
});

base.css:

body{
	/*background:#FF9D3C; */
	font-size:12px; 
	font-family:"宋体",Verdana, Arial;
	line-height:150%; 
	padding:0; 
	margin:0; 
	color:#2F2F2F;
	text-align: center;
}
div{
	margin:0 auto; 
	padding:0;
}
a{
	text-decoration:none;
	color:#2F2F2F;
}
a:hover{
	text-decoration:underline;
}

h1{
	text-align: center;
}


.nav_div{
	width: 100%;
	height: 50px;
	background-color: #07861B;
}
.nav{
	width: 1000px;
	height: 50px;
	line-height: 50px;
	margin: 0 auto;
	margin-bottom: 5px;
	list-style-type:none;
}

.nav li{
	float:left;
	position: relative; 
}
.nav li a{
	padding:10px 22px;
	font-family: "微软雅黑";
	color: white;
	font-weight: bold;
	font-size: 19px;
}
.nav li a:hover{
	background-color: #22c108;
    text-decoration: none;
    color: white;
}
.nav li.selected a{
	background-color: white;
}

.nav_child{
	list-style-type:none;
	width: 150px;
	position: absolute; /*--Important - Keeps subnav from affecting main navigation flow--*/
	left: 0; top: 45px;
	background: #07861B;
	margin: 0; padding: 0;
	display: none;
	float: left;
	border: 1px solid #111;
	font-size: 12px;
}
.nav_child li{
	width: 100%;
	height: 40px;
	line-height: 40px;
	margin: 0; padding: 0;
	border-top: 1px solid #252525; /*--Create bevel effect--*/
	border-bottom: 1px solid #444; /*--Create bevel effect--*/
	clear: both;
}
.nav_child li a{
	font-size: 12px;
}