<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>XXsystem</title>
<link href="http://netdna.bootstrapcdn.com/bootstrap/3.1.1/css/bootstrap.min.css" rel="stylesheet">
</head>
<body>
<nav class="navbar navbar-default navbar-fixed-top " role="navigation">
<div>
<div>
<button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1">
<span>Toggle navigation</span>
<span></span>
<span></span>
<span></span>
</button>
<a href="#">SuJueNet</a>
</div>
<div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
<ul class="nav navbar-nav">
<li><a href="#">首页</a></li>
<li>
<a href="#" data-toggle="dropdown">功能<span></span></a>
<ul role="menu">
<li><a href="#">aaaaaa</a></li>
<li><a href="#">bbbbbbbb</a></li>
<li><a href="#">ccccccccccc</a></li>
<li><a href="#">ddddddd</a></li>
<li></li>
<li><a href="#">eee</a></li>
<li><a href="#">fffff</a></li>
</ul>
</li>
<li><a href="#">帮助</a></li>
</ul>
<script src="http://cdn.bootcss.com/jquery/1.11.1/jquery.min.js"></script>
<script src="http://cdn.bootcss.com/bootstrap/3.2.0/js/bootstrap.min.js"></script>
</body>
</html>
开启兼容模式
把你的浏览器编码格式改成utf-8试试