Abstract: Air cushion characteristics of pneumatic cylinders are studied experimentally. A computer aided pneumatic cylinder testing system was developed. Pressures in the cushion chambers, in inlet and outlet pipelines, cylinder displacement and shock acceleration were tested under different working conditions by tuning the source pressure and opening of the cushion needle valve. Typical air cushion characteristics including over cushioning, deficient cushioning and optimum cushioning were analysed. It was proved that the mechanical collision between the piston and the end cap was the main cause of shock, and there existed mechanical collisions that worsen the cushion performance in some deficient cushionings, and air cushion is only applicable under certain working conditions.