简单三级联动

<select id="department">
    <option>----请选择部门----</option>
    <option>市场部</option>
    <option>技术部</option>
    <option>行政部</option>
</select>
<select class="bu">
    <option>----请选择分部----</option>
</select>
<select style="display: none" class="bu">
    <option>1部</option>
    <option>2部</option>
    <option>3部</option>
</select>
<select style="display: none" class="bu">
    <option>4部</option>
    <option>5部</option>
</select>
<select style="display: none" class="bu">
    <option>6部</option>
    <option>7部</option>
    <option>8部</option>
</select>
<select class="personnel">
    <option>----请选择人员----</option>
</select>
<select style="display: none" class="personnel">
    <option>小明</option>
    <option>小花</option>
    <option>小强</option>
    <option>小雨</option>
    <option>小雪</option>
</select>
<select style="display: none" class="personnel">
    <option>明明</option>
    <option>花花</option>
    <option>强强</option>
    <option>雨雨</option>
    <option>雪雪</option>
</select>
<select style="display: none" class="personnel">
    <option>明</option>
    <option>花</option>
    <option>强</option>
    <option>雨</option>
    <option>雪</option>
</select>

    <script type="text/javascript">
        $(document).ready(function(){
            $("#department").change(function(){
                $("#department option").each(function(i,o){
                    if($(this).attr("selected")){
                        $(".bu").eq(i).show();
                        $(".bu").eq(i). siblings(".bu").hide()
                    }
                    $(".bu").change(function(){
                        $(".bu option").each(function(i,o){
                            if($(this).attr("selected"))
                            {
                                $(".personnel").eq(i).show();
                                $(".personnel").eq(i). siblings(".personnel").hide()
                            }
                        });})
                });

            });

        });


    </script>