Aimed at the problem of inadequate load-bearing capacity of the traditional cylindrical hydraulic piston,a rectangular piston was proposed and its sealing performance under different working conditions was investigated.Based on Abaqus software,the finite element model of the special-shaped piston was established to study the influence of medium pressure,sealing gap,piston motion state and friction coefficient on the sealing performance,and the stress distribution and overturning of the special-shaped sealing ring at different positions were analyzed.The results show that the higher the medium pressure,the higher the maximum Mises stress and the maximum contact stress of the seal ring; the smaller the seal gap,the higher the maximum Mises stress and the maximum contact stress.Compared to the static seal,the maximum Mises stress and maximum contact stress both increase significantly during the internal stroke and increase with the friction coefficient.However,the difference between the maximum Mises stress and the maximum contact stress in the external stroke is relatively small compared to the static seal.The maximum stress values under all working conditions occur in the circular arc section of the sealing ring.During the movement of the piston,the sealing ring did not flip,but there is a displacement in its position.The results prove the feasibility of the special-shaped piston and its good sealing performance,and provide a basis for the design and optimization of the piston structure.