A blind-rivet gun includes a gun header, a cylinder, a piston, and a tube. The cylinder is separated from the gun header. The piston includes a piston header. The piston header and an inner surface of the cylinder form a seal to divide the cylinder into a first air chamber and a second air chamber. The cylinder includes a first gas hole and a second gas hole. The first gas hole is connected to the first air chamber, and the second gas hole is connected to the second air chamber. The piston is adapted to slide in the cylinder to generate inner high pressure gas by alternatively supplying outer high pressure gas to the first gas hole or the second gas hole. The tube is connected to the gun header and the cylinder. The tube transmits inner high pressure from the cylinder to the gun header.