My websites ranking well in Yahoo, Bing but not in Google, even showing on 1st page in Bing and Yahoo ...please explain what is the reason?
That's normally the case I'm afraid. It's quite easy to rank in Yahoo/Bing without much effort but Google is a lot more sophisticated. It's worth visiting their site to get a better idea of how they rank sites so that you can tailor a strategy to rank better in Google - https://support.google.com/webmasters/answer/70897?hl=en
the reason is that they have different databases and rules, that's all. (obvious). anyway, let's not consider Bing/Yahoo a secondary engine. It's a very good service, and we should focus on it much much more.