The utility model provides a pneumatic actuating mechanism with damping, which can solve the problem that the existing pneumatic actuating mechanism can not meet the closing requirement of a valve ona pressure swing adsorption device, so that the sealing failure of the valve can be caused. The air cylinder comprises an air cylinder body, cylinder covers are respectively mounted at two axial endsof the cylinder body; Two oppositely-arranged pistons and an output shaft located between the two pistons are arranged in the air cylinder body. Racks parallel to the axial direction of the air cylinder body are installed on the opposite side faces of the two pistons correspondingly. the two racks are simultaneously meshed with a gear sleeved on the output shaft; a cylinder body of the air cylinder is respectively provided with an air source channel I communicated with the inner side areas of the two pistons and an air source channel II communicated with the outer side areas of the two pistons; the hydraulic buffer device is inserted and fixed in the middle of the air cylinder cover and is sealed with the air cylinder cover through an O-shaped ring, the axial direction of the hydraulic buffer device is parallel to the moving direction of the piston, and a collided head of the hydraulic buffer device is opposite to the piston on the same side.