I feel pain at ass hole when i go to toilet.. i check with doctor they said there is no piles.. i want know about it?

If it's not a pile..: There are lots of other things that could cause pain most commonly anal fissure. Although fistula, abcess and others are possible. I suppose your doc already ruled those out as they are usually obvious.

Likely a "fissure".: If you have pain in the anus when you are passing a stool that stretches it and no hemorrhoids(piles) were found, you likely have a very tiny tear - an "anal fissure". Treatments: hot sitz bathes, a high fiber diet +10+ cups of water daily and stool softeners to reduce hardness of stool is the first step. Topical Nitroglycerin cream/ointment twice a day to the anus will heal in 6 weeks or less.

See a specialist: If you are still having pain and your primary care physician could not tell what the source was, consider seeing a specialist for this (colon and rectal surgeon). The first thing that comes to mind is anal fissure, however i would not make any diagnosis without discussing in detail at length and doing a thorough exam. There are many things that can cause pain in the anal region.