不处理时，当SELECT 渲染后，无法自动回发，可以如下操作：

<asp:DropDownList ID="ddlSearchProvince" runat="server" lay-filter="searchprovince" AutoPostBack="true" OnSelectedIndexChanged="ddlSearchProvince_SelectedIndexChanged"></asp:DropDownList>
<asp:DropDownList ID="ddlSearchCity" runat="server"></asp:DropDownList>

<script>
        $(function () {
            //监听选择框
            layui.use(['form', 'laydate'], function () {
                var form = layui.form;
                form.on('select(searchprovince)', function (data) {
                    __doPostBack("ddlSearchProvince", "");
                });
                form.on('select(searchmachine)', function (data) {
                    __doPostBack("ddlSearchMachine", "");
                });

                form.render();
            })
        })
    </script>

如里不想使用Layui渲染，可以这样处理：

<asp:DropDownList ID="ddlTableName" CssClass="layui-select" runat="server" lay-ignore>
</asp:DropDownList>

在后面加一个“ lay-ignore  ”  ,  即可