string  url = "http://com.m9ms.com/click.aspx?id=9999&logo=3&zhon=中文";      
         System.Web.UI.HtmlControls.HtmlGenericControl script = new System.Web.UI.HtmlControls.HtmlGenericControl("script");
         script.Attributes.Add("type", "text/javascript");
         script.Attributes.Add("src", url);
         script.Attributes.Add("charset", "gb2312");
         this.form1.Controls.Add(script);

 <script type="text/javascript" src="http://com.m9ms.com/click.aspx?id=9999&amp;logo=3&amp;zhon=中文" charset="gb2312"></script>