An inflatable pneumatic bag includes two outer films up-down stacked, and two inner films located between them. By thermal-sealing means, an interval line is formed between upsides and downsides of the two inner films, while a pneumatic passage is formed between the upsides of the two inner films and the interval line. Air tubes are formed between downsides of the two outer films and the interval line, while the two inner films are bonded at the interval line to form air ingress for connecting through the pneumatic passage and the air tube. After thermal-sealing upsides of the two outer films and the interval line, a buffer space is formed between the outer films and the two films. When the air of the air tube is leaking to the buffer space, the air of the buffer space will press the inner films to seal the pneumatic passage and prevent from leaking.