$(function () {
        $("#btn").click(function () {
            var usercode = $("#UserCode").val();
            var verifycode = $("#Verifycode").val();
            if ($.trim(usercode) == "" || $.trim(verifycode) == "") {
                alert(" 您的[客户号]或者[验证码]必须填写！");
                return false;
            }
            else {
                document.SearchForm.action = '/index/Search?u=' + usercode;
                document.SearchForm.submit();
            }
        });
    });

<form id="SearchForm" name="SearchForm" method="post">
 ……
</form>