The finite element model of YO-shaped combined seal was established by ABAQUS software.The static contact pressure and Mises stress distribution in the seal area were compared between Y-shaped composite seal and Y-shaped seal,two Y-shaped composite seals made of polyurethane and nitrile rubber(NBR) materials.The influences of O-ring diameter on the performance of Y-shaped combined seal made of the two materials were analyzed.The results show that the contact pressure and Mises stress of Y-shaped combined seal in the sealing area are greater than those of Y-shaped ring with the same specification and material during the instroke and outstroke of the piston rod,and the increase of contact pressure of the Y-shaped combined seal is more obvious and the stress distribution is more uniform during the outstroke of the rod,which verifies the characteristics of the double sealing and the improvement of root tear resistance of Y-shaped combined seal.When the O-ring diameter is the same,the maximum contact pressure difference between the outstroke and instroke of the polyurethane combined seal is much higher than that of the NBR combined seal,while the Mises stress distribution of the NBR combined seal is more uniform.With the increase of the O-ring diameter,the maximum contact pressure of the polyurethane combined seal increases first and then decreases,while the maximum contact pressure of the NBR combined seal gradually decreases.But the Mises stress of both show a gradually increasing trend,and the increase in NBR combined seal is more significant.The research results provide a reference for the selection of seals under different working conditions.