The invention discloses a pneumatic punching machine. The pneumatic punching machine comprises support frames and a crank arm structure matched with the support frames. The crank arm structure comprises slide rails, a sliding block, a crank arm, a stroke adjusting mechanism and an air cylinder, wherein the slide rails are vertically arranged between the two adjacent sidewalls of the support frames; the sliding block is in sliding fit with the slide rails; one end of the crank arm is hinged to the upper end of the sliding block; the stroke adjusting mechanism is hinged to the bent part of the crank arm; the air cylinder is hinged to the other end of the crank arm; and the lower end of the sliding block is provided with a punch shank. Through the arrangement of the crank arm and push and pull of the air cylinder, punching force of the punch shank can be effectively increased; the stroke of the punching machine can be adjusted conveniently and rapidly through the stroke adjusting mechanism hinged to the bent part of the crank arm, so that the pneumatic punching machine meets the requirements of workpieces of different strokes. The pneumatic punching machine is large in punching force, high in punching efficiency and adjustable in punching stroke.