Abstract: Metro vehicle auxiliary system charger module provides low-voltage power supply for the whole vehicle. To ensure that the vehicle can quickly return to the working state after being disturbed, fault reset mechanism needs to be added to the control software. Taking the auxiliary system of Suzhou Rail Transit Line 4 as the object, the reason of charger driver board straight through fault is analyzed, and the solution of adding fault reset mechanism in vehicle auxiliary system control software is proposed. Based on reliability experiment, optimization of fault reset mechanism is carried out. The experiment proves that the optimized fault reset mechanism can solve the driver board straight through problem effectively.