<a href="#">博客</a>
<div class="nav-down">
<a href="#">精彩博文</a>
<a href="#">博客专栏</a>
<a href="#">博客专家</a>
<a href="#">我的博客</a>
</div>
</li>
<li>
<a href="#">商城</a>
<div class="nav-down">
<a href="#">软件商城</a>
<a href="#">C币商城</a>
<a href="#">C币充值</a>
</div>
</li>
<li>
<a href="#">下载</a>
<div class="nav-down">
<a href="#">资源分类</a>
<a href="#">我的资源</a>
</div>
</li>
</ul>
</div>
第一种：css3实现
*{
margin:0px;
padding:0px;
font-family: "Microsoft Yahei", Helvetica, sans-serif, Lato;
}
li{
list-style: none;
}
a{
text-decoration: none;
}
.nav{
width:100%;
height: 40px;
margin-top:50px;
background-color: #222;
}
.nav .nav-list{
width: 1000px;
height: 40px;
margin:0 auto;
}
.nav .nav-list li{
float: left;
position: relative;
}
.nav .nav-list li > a{
display: block;
height: 40px;
line-height: 40px;
padding:0 30px;
color:#aaa;
width:60px;
}
.nav .nav-list li:hover>a{
color:#fff;
background-color: #333;
}
<span style="color:#ff0000;">.nav .nav-list li:hover .nav-down{
display: block;
}</span>
.nav-down{
width:150px;
background-color: #333;
position: absolute;
top:40px;
left:0px;
display: none;
}
.nav .nav-list .nav-down a{
display: block;
line-height: 30px;
color:#aaa;
padding-left:30px;
}
<span style="color:#ff0000;">.nav .nav-list .nav-down a:hover{
color:#fff;
background-color: #333;
}</span>实现方法很简单，即刚开始让下拉的菜单隐藏，然后当鼠标经过的时候，将隐藏的菜单显示即可，具体实现代码如上的红色部分，这里不作详细讲解，代码很简单。
第二种：用jquery实现。
css:
*{
margin:0px;
padding:0px;
font-family: "Microsoft Yahei", Helvetica, sans-serif, Lato;
}
li{
list-style: none;
}
a{
text-decoration: none;
}
.nav{
width:100%;
height: 40px;
margin-top:50px;
background-color: #222;
}
.nav .nav-list{
width: 1000px;
height: 40px;
margin:0 auto;
}
.nav .nav-list li{
float: left;
position: relative;
}
.nav .nav-list li > a{
display: block;
height: 40px;
line-height: 40px;
padding:0 30px;
color:#aaa;
