可以用 RSS.Net 这个开源组件来实现

RssChannel channel = new RssChannel();

                RssItem item = new RssItem();

                item.Title = news.Title;
                item.Description = news.Description;
                item.PubDate = news.NewsTime;

                channel.Items.Add(item);

        RssFeed feed = new RssFeed();
        feed.Channels.Add(channel);
        Response.ContentType = "text/xml";

        channel.Title = feedName + " News";
        channel.Description = feedName + " News";
        channel.LastBuildDate = channel.Items.LatestPubDate();
        channel.Link = new Uri(rssUrl + fileName);

        feed.Write(Response.OutputStream);
        Response.End();