By changing the structural type of the servo cylinder combined seal,the simulation models of the two seal rings were established. Under the static seal state, the influences of the medium pressure, compression rate and contact friction coefficient on the seal performance of the servo hydraulic cylinder were explored by using ANSYS Workbench software. The maximum Von-Mises stress of the seal ring and the maximum contact pressure of the contact surface were taken as the judgment basis for the seal performance. Under the dynamic sealing state, a mathematical model for the leakage and the starting pressure was established, and the values of the leakage and the starting pressure were taken as the judgment basis of the sealing performance, so that the composition and structural parameters of the sealing ring were optimized. The results show that the maximum Von-Mises stress and the maximum contact pressure of the contact surface of the hydraulic cylinder with Ⅰ-ring are obviously better than those of the hydraulic cylinder with O-ring when any one of the parameters is changed under the static sealing state;however, under the dynamic sealing state, with the increase of the medium pressure, the leakages of the hydraulic cylinders of the two models are continuously reduced, the starting pressures are continuously increased, and the leakage of the hydraulic cylinders containing Ⅰ-rings is less, thus indicating that the sealing performance of Ⅰ-rings is optimized to that of O-rings.The studied Glyd ring combined with Ⅰ-shaped ring can provide reference for hydraulic cylinder designers.