觉得应该是这个顶部的CSS出了点问题...

先把顶部的代码贴出来。

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="Title.ascx.cs" Inherits="MedicineWeb.User.MasterPage.Title" %>
<div style="vertical-align: top;">
<div style="background-color: #A0FDB0;">
<img alt="Logo" src="/MedicineWeb/Image/Logo.jpg" width="600px" height="90px" />
</div>
<div id="HeaderDiv_Memu">
<ul class="HeaderDiv_Ul">
<li><a style="width: 166px; text-align: center">商品导航</a></li>
<li><a href="/MedicineWeb/User/CompanyIntro.aspx">首页</a></li>
<li><a href="/MedicineWeb/User/CompanySummarize.aspx">公司简介</a></li>
<li><a href="/MedicineWeb/User/News.aspx">新闻动态</a></li>
<li><a href="/MedicineWeb/User/Product.aspx">产品中心</a></li>
<li><a href="/MedicineWeb/User/Job.aspx">人才招聘</a></li>
<li><a href="/MedicineWeb/User/ContactUs.aspx">联系我们</a></li>
</ul>
</div>
</div>
<style type="text/css">
#HeaderDiv_Memu
{
padding: 0px;
margin: 0px;
height: 40px;
width: 100%;
margin: 0px auto;
}
.HeaderDiv_Ul
{
padding: 0px;
margin: 0px auto;
height: 40px;
list-style: none;
background-color: #61E078;
}
.HeaderDiv_Ul li
{
height: 40px;
line-height: 40px;
float: left;
vertical-align: middle;
text-decoration: none;
}
.HeaderDiv_Ul li a
{
font-family: @Adobe 黑体 Std R;
font-size: 16px;
font-weight: bold;
color: White;
height: 40px;
line-height: 40px;
float: left;
padding: 0px 20px 0px 20px;
margin:0px 0px 0px 0px;
vertical-align: middle;
text-decoration: none;
}
.HeaderDiv_Ul li a:hover
{
height: 40px;
line-height: 42px;
float: left;
padding: 0px 20px 0px 20px;
vertical-align: middle;
text-decoration: none;
cursor: hand;
background-color: #2B5834;
display: block;
}
</style>