In order to solve the sealing problem of the warm isostatic press on the condition of high pressure of 200 MPa and high temperature of 300 ℃,the Lshape seal structure composed of Lshape metal ring and Oshape rubber ring was designed,and the Lshape combined sealing structure model was established and assembled through ABAQUS.The thermomechanical coupling model of sealing structure was established to simulate the temperature and pressure load,and the stressstrain distribution regularity of Lshape seal structure was obtained by simulation analysis.The simulation results show that the Lshape seal structure can meet the sealing requirements of hightemperature and ultrahigh pressure conditions,for it can realize the sealing by Oring under low pressure condition and by Lshape combined sealing structure under high pressure condition.Aimed at the problem that the maximum stress exceeds the allowable stress of the material in the simulation analysis,the optimization design of the Lshape combined seal structure was carried out.After optimization,the maximum stress of the Lshape seal structure under high load condition is less than the allowable stress of the working cylinder and the end closure,and the contact pressure is larger than the working pressure,which can achieve a good seal effect.