High-pressure valves may fail due to cracks, leakage and fatigue failure after a short period of time when they are under high temperature and high pressure conditions for a long time, where they also need to bear the coupling effects of temperature field, flow field and pressure field. In order to improve the fatigue reliability of high-pressure valves, based on the fatigue cumulative damage theory, the fatigue life of valves under coupling action can be obtained by using the nominal stress method. Moreover, the simulation by ANSYS simulation software helps to work out the distribution law of temperature field and stress field of valves working steadily under high temperature and high pressure. The simulation results show that the most likely damaged area is the corner of the entrance and exit of the valves near the cone groove, which can be improved by thermal spraying to reduce the structural mutation, increase the transition fillet to make the structural strength distribution uniform, and select more suitable materials so as to improve the reliability of the valves.