SOURCE

$(".demo-nav1-items li").hover(function() {
  var index = $(this).data("index");
  var left = index * 110 + 5;
  $(".demo-nav1-line").css({
    "margin-left": left + "px",
    "transition": "all .3s"
  });
},
function() {
  //鼠标移开后，下划线回到选中的导航下面
  var active_index = $(".demo-nav1-items").find(".active").data("index");
  var left = active_index * 110 + 5;
  $(".demo-nav1-line").css({
    "margin-left": left + "px",
    "transition": "all .3s"
  });
})

$(".demo-nav1-items").on("click", "li", function() {
  $(this).siblings().removeClass("active");
  $(this).addClass("active");
})

<div class="demo-nav1">
  <h3>
    导航下划线随鼠标移动
  </h3>
  <ul class="demo-nav1-items">
    <li data-index="0" class="active">
      <a> 导航一</a>
    </li>
    <li data-index="1">
      <a>导航二</a>
    </li>
    <li data-index="2">
      导航三
    </li>
    <li data-index="3">
      导航四
    </li>
    <li data-index="4">
      导航五
    </li>
    <span class="demo-nav1-line">
    </span>
  </ul>
</div>
<script src="http://libs.baidu.com/jquery/2.0.0/jquery.min.js">
</script>

html,
body,
div,
ul,
li {
  margin: 0;
  padding: 0;
}

html,
body {
  width: 100%;
  height: 100%;
}

ul {
  list-style: none;
}

.demo-nav1 {
  text-align: center;
  position: relative;
  margin-top: 5px;
  width: 100%;
  height: 150px;
  border: 1px solid#5FB878;
}

.demo-nav1-items {
  width: 550px;
  height: 53px;
  position: absolute;
  left: 50%;
  margin-left: -225px;
  overflow: hidden;
}

.demo-nav1-items li {
  float: left;
  width: 100px;
  text-align: center;
  position: relative;
  cursor: pointer;
  transition: all .2s;
  height: 50px;
  line-height: 50px;
  margin: 0 5px;
}

.active {
  border-bottom: 3px solid#5FB878;
  color: #5FB878;
}

.demo-nav1-line {
  position: absolute;
  display: inline-block;
  width: 100px;
  height: 3px;
  bottom: 0;
  left: 0;
  margin-left: -100px;
  background-color: #5FB878;
}