High-voltage switch is a key component to discharge circuit. Nevertheless，the voltage on the high-voltage switch in discharge circuit appears transient sometimes，which will cause the spurious triggering or breakage of the high-voltage switch. Furthermore，the abnormity of the high-voltage switch will cause the failure of the discharge circuit. The reason of this kind of failure was explored in this study. The circuit was simulated and analysed. A protection method was proposed to solve this problem according to simulation results. Practical tests were employed on the real circuit，which validated the simulation results and the effectiveness of the protection method.