In google webmaster there is option as u know Links to your site in that it shows me 7 external links, but when in google i look back links by site: it shows me 0 link. kindly suggest me on this ...
I assume you mean not site: but link:, correct? (It's a different Google operator.) Don't worry about link: -- its purpose it merely illustrative. It normally returns just a small random sample of links to a site (Google doesn't want to give the full info to your competitors!). Since you have very few backlinks right now, link: returns nothing. It will start returning something as you build more links, but just don't worry about it at all. The info in Google Webmaster Tools is much more complete. Google tells you that you see all your backlinks there. It isn't true (!), but it's a much larger sample. You may be able to see additional links in Yahoo Site Explorer (just use link: in Yahoo and it will take you there). But make sure you filter out the links from your own domain. I hope this helps!
That is totally normal. It's just the way google works. Google search only shows a SMALL sample of baclinks. Webmaster Tools shows a bigger sample of backlinks.