A simulation model for the dynamic characteristics of pressure relief valve was established based on AMESim in this paper to solve the problem of the abnormal outlet pressure fluctuation during the −40℃ environmental test of the pressure relief valve of the booster delivery system of a certain type of launch vehicle. By calibrating the model with test data and parameters of the valve and test system and using the Stribeck friction model, the simulation successfully reproduced the pressure fluctuation phenomenon, located the cause of the failure and showed the main reason for the long-term drop in pressure. To solve the problem, the proposed improvement scheme of the high-pressure sealing structure was simulated and verified by experiments.