Hyperbolik, technically you could design your website using RSS, you could transform the RSS feed using XSLT into HTML and then apply style or parse or embed the data into the main body of a news page (for example). Though I am unsure exactly what the OP is trying to accomplish in terms of design.
RSS data length is so big. users load time is long.
Err, nope it doesn't, RSS Feeds require less markup than any HTML document I have ever come across, the only time the length of the feed would be "big" is if you didn't provide a "cut off point" as to how far back your news stories and announcements go, and that's just a bad idea.