<input id="dd" type="text" class="easyui-datebox" required="required" ></input>
<asp:Button ID="Button1" runat="server" Text="Button" />

 $("#Button1").click(function () {
        $("#dd").datebox("setValue", "7/1/2012");//设置默认值
        // var a=    $("#dd").datebox("getValue");//取值

    });