<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>demo</title>
<style>
* { margin:0; border:0; padding:0; list-style:none; list-style-type:none;}
.nav { width:1000px; float:left;}
.nav li { float:left; width:99px; margin-right:1px; display:inline;}
.nav li span { display:block; width:99px; height:30px; line-height:30px; text-align:center; background:#C03; cursor:pointer;}
.nav li p { top:30px; left:0; width:99px; height:auto; display:none;}
.nav li p a { display:block; width:99px; height:28px; line-height:28px; text-align:center; margin-top:1px; background:#F03; color:#fff;}
.nav li:hove span { background:#30F;}
.nav li:hover p { display:block;}
.nav li p a:hover { background:#36F;}
.bga { float:left; background:#336; width:100%; height:100px; color:#fff;}
</style>
</head>
<body>
<ul class="nav">
<li><a href="#"><span>频道1</span></a>
<p><a href="#">频道1-1</a><a href="#">频道1-2</a><a href="#">频道1-3</a><a href="#">频道1-4</a></p>
</li>
<li><a href="#"><span>频道2</span></a></li>
</ul>
<div class="bga">111</div>
</body>
</html>
上面是用li:hover实现的，下面用JS实际，在网上找了一个JQ的。
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>demo</title>
<style>
* { margin:0; border:0; padding:0; list-style:none; list-style-type:none;}
.nav { width:1000px; float:left;}
.nav li { float:left; width:99px; margin-right:1px; display:inline;}
.nav li span { display:block; width:99px; height:30px; line-height:30px; text-align:center; background:#C03; cursor:pointer;}
.nav li p { top:30px; left:0; width:99px; height:auto; display:none;}
.nav li p a { display:block; width:99px; height:28px; line-height:28px; text-align:center; margin-top:1px; background:#F03; color:#fff;}
.nav li.on span { background:#30F;}
.nav li.on p { display:block;}
.nav li p a:hover { background:#36F;}
.bga { float:left; background:#336; width:100%; height:100px; color:#fff;}
</style>
<script type="text/javascript" src="
http://mat1.gtimg.com/www/asset/lib/jquery/jquery/jquery-1.11.1.min.js"></script>
</head>
<body>
<ul class="nav">
<li><a href="#"><span>频道1</span></a>
<p><a href="#">频道1-1</a><a href="#">频道1-2</a><a href="#">频道1-3</a><a href="#">频道1-4</a></p>
</li>
<li><a href="#"><span>频道2</span></a></li>
</ul>
<div class="bga">111</div>
<script type="text/javascript">
$('.nav li').each(function(){
$(this).hover(function(){
$(this).addClass('on').siblings().removeClass('on');
});
});
</script>
</body>
</html>
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