My age is 21year old but am wieght is 85kg

Tummy fat is all about diet. Actually most fat is, but fat on the tummy is particularly linked to a diet high in sugar and refined carbs.

Cut out all the junk food, especially any thing deep fried or containing sugar. Also cut out cake, bread, pasta, rice, potatoes, box cereals. Eat lots of whole foods, esp eggs, oily fish, chicken, fresh meat, lots and lots of green veg, whole fruit (not juice) olive oil, nuts, wholegrains.

Watch your portion size. Most people eat 2 or 3 portions of rice and pasta at a time without realising it. One bagel is three portions of bread. Spend a little time measuring how much you are eating, so you have an idea of where you need to apply some control.

Eat when you are hungry, and only when you are hungry. Don't eat because it's coffee break, or your friend offers you candy, or because Glee is on TV.

Try to be active generally, walk as much as possible, and go to bed on time.