<!DOCTYPE html><html lang="en"><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>html</title> <link rel="stylesheet" href="./rule/bootstrap-Normalize.css"> <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/css/bootstrap.min.css"> <script src="https://cdn.bootcss.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script></head><body> <nav class="navbar navbar-inverse navbar-fixed-top"> <div class="container"> <!-- Brand and toggle get grouped for better mobile display --> <div class="navbar-header"> <button type="button" class="navbar-toggle collapase" data-toggle="collapase" data-target="#bs-example-navbar-collapse-1" aria-expanded="false"> <span class="sr-only">Toggle navigation</span> <span class="icon-bar"></span> <span class="icon-bar"></span> <span class="icon-bar"></span> </button> <a class="navbar-brand" href="#">Brand</a> </div> <!-- Collect the nav links, forms, and other content for toggling --> <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1" > <ul class="nav navbar-nav"> <li class="active"><a href="#">Link <span class="sr-only"></span></a>Link</li> <li class="dropdown"> <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Dropdown <span class="caret"></span></a> <ul class="dropdown-menu"> <li><a href="#">Action</a></li> <li><a href="#">Another action</a></li> <li><a href="#">Something else here</a></li> <li><a role="separator" href="#"></a></li> <li><a href="#">Separated link</a></li> <li><a role="separator" href="#"></a></li> <li><a href="#">One more separated link</a></li> </ul> </li> </ul> </div> </div> </nav> <!-- jQuery (necessary for Bootstrap's JavaScript plugins) --> <script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script> <!-- Include all compiled plugins (below), or include individual files as needed --> <script src="https://cdn.bootcss.com/bootstrap/3.3.7/js/bootstrap.min.js"></script> <script src="main.js"> </script></body></html>解决方案
这是因为，Bootstrap的导航栏只是默认是51px高，而并非永远是51px高，如果其中有元素出现多行，是会将高度撑高的。
你的demo里，由于有一个标签多了一个Link，所以将整个导航栏撑高了20px。