The optimization research on the rotating dynamic seal O-ring in the hydraulic transmission system was conducted,and the final optimization results through simulation analysis and experiments were obtained.The O-ring model based on ABAQUS was established,and two kinds of nitrile rubber materials with the same hardness level and different mechanical properties were compared and analyzed.The contact stress and initial sealing performance of O-rings with different materials under medium load were studied.The test was employed to optimize the size of the O-ring.The results show that the size has little effect on the static hydraulic sealing performance,low-temperature sealing performance and high-temperature sealing performance of the O-ring,but has a greater impact on the dynamic sealing wear performance of the O-ring.The cross-sectional diameter is controlled within the lower limit of the design tolerance,the O-ring made of NBR material with good mechanical properties shows the best sealing performance.The research results obtained by combining simulation analysis and verification test provide technical support for the design and application of high-performing O-rings.