Abstract: Aiming at the sealing problem of O-ring in pneumatic balancer, the finite element analysis model was established by using ANSYS software, and the change law of stress under different precompression rate and working pressure was obtained. The results show that the maximum contact stress and von Mises stress of the sealing ring increase with the increase of the precompression rate and the working medium pressure. The sealing performance test platform of pneumatic balancer sealing ring was built. The leakage amount of the device was calculated by measuring the falling distance of the weight when it was finally stabilized. The sealing effect was checked by the leakage amount.