/*嵌套菜单样式*/
.dropdown-submenu{
    position:relative;
}

.dropdown-submenu>.dropdown-menu{
    /*嵌套菜单位置*/
    top:0;
    left:100%;
    /*将left的值换成负值可使嵌套菜单向右展开*/
    margin-top:-6px;
    margin-left:-1px;
}

.dropdown-submenu:hover>.dropdown-menu{
    display:block;
}

<ul class="nav nav-pills">
  <li class="active"><a href="##">首页</a></li>
  <li class="dropdown">
      <a href="##" class="dropdown-toggle" data-toggle="dropdown">教程<span class="caret"></span></a>
      <ul class="dropdown-menu">
          <li><a href="##">CSS3</a></li>
        <li><a href="##">Sass</a></li>
        <li><a href="##">jQuery</a></li>       
        <!--嵌套下拉菜单-->
        <li class="dropdown-submenu">
        <a href="##">嵌套选项1
            <span class="caret2"></span>
        </a>
            <ul class="dropdown-menu">
                <li>
                    <a href="##">C#</a>
                </li>
                <!--嵌套下拉菜单-->
                <li class="dropdown-submenu">
                    <a href="##">嵌套选项2
                        <span class="caret2"></span>
                    </a>
                    <ul class="dropdown-menu">
                        <li>
                            <a href="##">SQL</a>
                        </li>
                    </ul>
                </li>
                <li>
                    <a href="##">VB</a>
                </li>
            </ul>     
        </li>
        <li><a href="##">Responsive</a></li>
      </ul>
  </li>
 <li><a href="##">关于我们</a></li>
</ul>