Abstract: The reliability of the power distribution system of the trip solenoid valve is related to the safe operation of the steam turbine unit. Aiming at the problem of tripping solenoid valve malfunction caused by the action of the dual power switching device in the trip solenoid valve power distribution system, we analyzed the principle of malfunction of solenoid valve and failure of trip system. Considering from the aspects of canceling the power switching device and changing the power supply topology, two power supply improvement schemes were proposed. The dynamic fault tree and dynamic Bayes network were used to analyze the reliability of the trip solenoid valve power distribution system. The simulation results show that the proposed distribution system solves the problem of electromagnetic valve maloperation caused by power switching, improves power supply stability and makes the system have a high availability rate.