In order to investigate the properties of a new type of cast polyurethane elastomer (CPU) as O-ring retaining ring material,a two-dimensional symmetrical model of O-ring and retaining ring was constructed by using finite element analysis software.The performance of CPU material retaining ring in dynamic and static sealing state under 35 MPa dielectric pressure was analyzed,and was compared with that of polytetrafluoroethylene (PTFE) and thermoplastic polyester elastomer (TPEE) material retaining rings.The results show that the contact stress and sealing length of O-ring matched with CPU material retaining ring are slightly better than those of the other two material retaining rings,which can achieve better sealing effect.The maximum deformation of CPU material retaining ring in static and dynamic sealing state is the smallest,and the maximum von Mises stress of CPU material retaining ring is lower than that of the other two material retaining rings.The CPU material retaining ring has higher reliability and longer service life,which can effectively prevent the failure of O-ring such as extrusion and bite under high pressure.The bench test results show that the extrusion height of CPU retaining ring is much smaller than that of TPFE and TPEE retaining rings,which verifies the correctness of the finite element analysis results.It can be concluded that the new CPU retaining ring matched with O-ring can realize the dynamic and static sealing of hydraulic cylinder.