The piston of double acting round air cylinder can output force (thrust or pull) when it moves forward or backward. Simple structure and optional travel. The piston of double acting round air cylinder can output force (thrust or pull) when it moves forward or backward. The structure is simple, and the stroke can be selected according to the needs. If the cylinder is not equipped with buffer device, when the piston moves to the terminal, especially for the cylinder with long stroke, the force of piston striking the end cover is very large, which is easy to damage the parts.