I have a domain and google has in better rank my domain without www,my question is the only one thing that I have to do is select my prefered domain in google webmaster tools like domain.com or I need redirect with 301 www to domain.com ?
It's always best to choose one and stick with it consistently everywhere. It doesn't matter much which one you go for - as long as your consistent in your Webmaster Tools settings, inbound links and internal links. I'd recommend that if you're going to change from www.domain.com to just domain.com you 301 redirect all pages on www.domain.com to domain.com - and also review all of your internal links and inbound links to make sure they're pointing to domain.com instead of www.domain.com.
Great explanation @CarleIsEnstien. Just to piggy-back on your response. Most people will typically link to you using www. so pointing your site to a www.domain.com ensures you will get full link value with all those wonderful links.
As @carleisenstein said, it is best to stick the the same one throughout. with or without the www. makes no difference in SEO, but www. looks nicer IMO.