Your rankings for various keywords in google search results have dropped. That means , you many not be ranking for several keywords that you used to earlier.

This has been happening with lot of low quality sites after the EMD update on 28th. There are other updates after this EMD that may have affected your site. There were some minor updates on Panda/Penguin also.

Basically you lost the rankings in google search results. Thats the reason for drop in traffic.

Site health & no. of indexed pages have nothing to do with drop. You might have a very big website with thousands of indexed pages yet need not be any traffic to it.

Traffic depends on your rankings.

thank you Anil Kint. . Then its possible to boot up from feature updates ? or i want to bye new domain and work with that ?

Chances are you got hit by the EMD update. If so, it doesn't mean that your site is doomed, it just means that you may not get the benefit you were receiving before for exact match keywords. If your main keyword was "articles download" and you were hit by the EMD update, then that might explain your drop in traffic.

I would just keep adding quality content to your site, instead of worrying about if you should start over with a new domain or not.