<script src="js/jquery/1.11.1/jquery.min.js"></script>

<div class="top-title">这是顶部导航条</div>
<div class="margint"><p>滚动看效果</p><p>滚动看效果</p></div>

.top-title {background:#e74c3c;color:white;font-size:24px;padding:5px;text-align:center;position: fixed;left:0;top:0;width:100%;transition: top .5s;}
.hiddened{top: -90px;}
.showed{top:0;z-index: 9999;}

$(function(){  
  var winHeight = $(document).scrollTop();
 
  $(window).scroll(function() {
    var scrollY = $(document).scrollTop();// 获取垂直滚动的距离，即滚动了多少
 
    if (scrollY > 550){ //如果滚动距离大于550px则隐藏，否则删除隐藏类
      $('.top-title').addClass('hiddened');
    } 
    else {
      $('.top-title').removeClass('hiddened');
    }
 
    if (scrollY > winHeight){ //如果没滚动到顶部，删除显示类，否则添加显示类
      $('.top-title').removeClass('showed');
    } 
    else {
      $('.top-title').addClass('showed');
    }        
 
   });
});