工作实例：http://codepen.io/igcorreia/pen/htdxl

HTML

<div class="container">
    <div class="row">

        <p class="lead">Roll over the button on the left to see a dropdown</p>
        Rollover dropdown:
        <!-- Our Special dropdown has class show-on-hover -->
        <div class="btn-group show-on-hover">
          <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">
            Action <span class="caret"></span>
          </button>
          <ul class="dropdown-menu" role="menu">
            <li><a href="#">Action</a></li>
            <li><a href="#">Another action</a></li>
            <li><a href="#">Something else here</a></li>
            <li class="divider"></li>
            <li><a href="#">Separated link</a></li>
          </ul>
        </div>

        Regular dropdown:
        <!-- Single button -->
        <div class="btn-group">
          <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">
            Action <span class="caret"></span>
          </button>
          <ul class="dropdown-menu" role="menu">
            <li><a href="#">Action</a></li>
            <li><a href="#">Another action</a></li>
            <li><a href="#">Something else here</a></li>
            <li class="divider"></li>
            <li><a href="#">Separated link</a></li>
          </ul>
        </div>
    </div>

CSS

body{
    padding:10px;
}

.show-on-hover:hover > ul.dropdown-menu {
    display: block;    
}