<script language="javascript" type="text/javascript">
    if (window.self != window.top) {
        window.top.location = window.location;
    }
</script>

------解决方案--------------------

有a.aspx页面,<iframe>中是b.aspx页面,
则在b.aspx页面的Page_Load中:
C# code
        if (Request.ServerVariables["HTTP_REFERER"] == null)
        {
            Response.Redirect("a.aspx");
        }
        else
        {
            string urlPre1 = "http://" + Request.ServerVariables["HTTP_HOST"].ToString();
            string urlPre2= Request.ServerVariables["SCRIPT_NAME"].ToString();
            urlPre2 = urlPre2.Substring(0, urlPre2.Length - 6)+"a.aspx";//注意-6是b.aspx的长度
            if (urlPre1 + urlPre2 != Request.ServerVariables["HTTP_REFERER"].ToString())
                Page.ClientScript.RegisterStartupScript(Page.GetType(), "", "window.open('a.aspx')", true);
        }