@CHARSET "UTF-8";
#div{
margin-bottom:10px;
position:relative;
}
#div1{
width:153px;
padding-top:0px;
padding-left:0px;
position:absolute;
}
#div1 ul{
margin-top:0px;
padding-left:0px;
background-color:#ccc;
list-style:none;
}
#div1 ul li{
padding-left:0px;
}
#div1 ul li input{
margin-left:15px;
}
.close{
display:none;
}
.open{
display:block;
}

$(function(){
var position = $("#xx").position();
$("#div1").offset({ top:position.top+35,left:position.left+10});
$("#xx").click(function(){
$("#NG").toggleClass("open");
});

$("#div1 input[name=ng]").click(function(){
var arr = new Array();
$("input[name=ng]:checked").each(function(key,value){arr[key]=$(value).val();});
$("#xx").val(arr.join(","));
});
});

<div id="div">
<div align="center" id="div2" >
<form id="form1">
<input type="text" readonly="readonly" id="xx"/>
<input type="submit" value="查詢"/>
</form>
</div>
<div id="div1">
<ul class="close" id="NG" >
<li><input type="checkbox" name="ng" value=1 />1</li>
<li><input type="checkbox" name="ng" value=2 />2</li>
<li><input type="checkbox" name="ng" value=3 />3</li>
</ul>
</div>
</div>