Why do my site lost its rank on Google?
 

In the past few months, my site is top 10 on SERPs. But now it is very far.
Any suggestions that can help is much appreciated.

post quality means very new content in your website so it will be better helpful to higher the SERPs.

It;s because you might did over SEO for your site and after new update of Google panda out you might be penalized for over optimization :)

nice post thanks.

I think you should do linkbuilding to relevant and high pr websites in order to rank higher..

The most probable reason for the drop seems violation of guidelines (or some sort of penalty). Here is Matt Cutts helping you with other possible reason for the drop in SERP rankings...
http://www.youtube.com/watch?feature...&v=gx04qNrCbnk

may be Its due to your keyword competition or backlinks. You have to build good links with hew content.

Your site lost its ranking on google may be due to increase in keyword search competition. May be your competitor sites get the more backlinks than your site and also it from high pr sites.