A reciprocating pneumatic tool has a main tool body, a suspension internal slider and a rear damping spring. A front buffer air chamber is formed the main tool body and the suspension internal slider. A by-pass air supply passage is set into the cylinder wall of the main tool body and is arranged at interval with the hollow chamber along its extension. Both ends of the by-pass air supply passage have a first and a second venting end. The first venting end is linked to the air control valve chamber of the air pressure control module, and the second venting end is linked to the front buffer air chamber. Air pressure passing through air control valve chamber can be guided the through by-pass air supply passage, so the front buffer air chamber accumulates air pressure to generate a damping effect on the front end of the suspension internal slider.