In order to solve the problem that the protection performance of special vehicles is greatly reduced when the three-proof system fails or the state is abnormal, which seriously affects the personal safety of the personnel in the vehicle, a fault tree model of the three-proof system is established. Through in-depth analysis of the working principle and common faults of the three-proof system, quantitative and qualitative analysis of the fault tree model is performed, and the analysis of structural importance is completed. The results show that this method can quickly locate the faults of the three-proof system, effectively shorten the troubleshooting time and improve the maintenance efficiency.