My dad have this big belly not fat it's more like a ballon i swear , he have no constipation or anything and he is not fat . please help . ?

Many causes...: A distended or protuberant abdomen in a man has many potential causes. One serious cause might be cirrhosis of the liver that can result in accumulation of fluid in the abdominal cavity distending the belly or abdomen. Another is excessive visceral fat (belly fat) wrapping around the abdominal organs. I suggest your father go see his doctor.

Concern for ascites: My initial impression based upon the description may be that your father may have ascites which is fluid in the abdomen. Typical causes relate to liver diseases such as hepatitis. Other causes may relate to lymphatic or venous congestion in the abdomen. This needs to be evaluated by lab work and either a sonogram or ct of the abdomen.