$('#j_dateStart').datebox('setValue', "");　　　　//赋予空值

 $("#j_dateStart").datebox("getValue");　　　　//获取值

<input class="easyui-datetimebox" name="operDateStart" id="j_dateStart" data-options="editable:false" style="width:150px">

 <!--条件检索-->

    <div data-options="region:'north',title:'搜索条件',split:true,border:false,collapsed:true" style="height: 108px; overflow: hidden;">

        <form id="searchForm">

            <table class="tableForm datagrid-toolbar" style="text-align: right; font-weight: bold;">

                <tr>

                    <td style="width:100px;"><label>标题:</label></td>

                    <td><input name="hTitle" style="width: 308px;" /></td>

                    <td></td>

                    <td></td>

                </tr>

                <tr>

                    <td style="width:100px;"><label>操作日期:</label></td>

                    <td>

                        <input class="easyui-datetimebox" name="operDateStart" data-options="editable:false" style="width:144px">

                        <label>至</label>

                        <input class="easyui-datetimebox" name="operDateEnd" data-options="editable:false" style="width:144px">

                    </td>

                    <td style="width:40px;"></td>

                    <td align="left">

                        <a href="javascript:void(0);" class="easyui-linkbutton" data-options="iconCls:'fa fa-search'" onclick="SearchFilter();">搜索</a>

                        <a href="javascript:void(0);" class="easyui-linkbutton" data-options="iconCls:'fa fa-undo'" onclick="ClearSearch();">清空</a>

                    </td>

                </tr>

            </table>

        </form>

    </div>

<div data-options="region:'north',title:'搜索条件',split:true,border:false,collapsed:true" style="height: 115px; overflow: hidden;">

        <form id="searchForm">

            <table class="tableForm datagrid-toolbar" style="font-weight: bold;">

                <tr>

                    <td colspan="">姓名:<input name="name" id="j_name" style="width:150px" />&nbsp;性别:<input name="sex" id="j_sex" style="width:150px" />&nbsp;宿舍楼:<input name="romNumber" id="j_romNumber" style="width:150px" /></td>

                </tr>

                <tr>

                    <td>操作日期:</td>

                    <td style="width:400px;">

                        <input class="easyui-datetimebox" name="operDateStart" id="j_dateStart" data-options="editable:false" style="width:150px">

                        至

                        <input class="easyui-datetimebox" name="operDateEnd" id="j_dateEnd" data-options="editable:false" style="width:150px">

                    </td>

                    <td>

                        <a href="javascript:void(0);" class="easyui-linkbutton" data-options="iconCls:'fa fa-search'" onclick="SearchFilter();">搜索</a>

                        <a href="javascript:void(0);" class="easyui-linkbutton" data-options="iconCls:'fa fa-undo'" onclick="ClearSearch();">清空</a>

                    </td>

                </tr>

            </table>

        </form>

    </div>