It is easy to get this feature, simply add a panel to the bottom of propertygrid. The code below shows how to use layout component integrate them together.
<div class="easyui-layout" style="width:300px;height:300px">
<div region="center" border="false">
<table id="pg" class="easyui-propertygrid" data-options="
data:data,
fit:true,
showGroup:true,
scrollbarSize:0
">
</table>
</div>
<div region="south" split="true" style="height:50px">
</div>
</div>