Research on the problem of frequent failures of the potential transformer in the operation of the rolling stock concludes that the aging of the insulation in the natural environment and the influence of overvoltage and overcurrent on the insulation are the main reasons for the failure of the potential transformer, and the theoretical analysis is proved by simulation based on the finite element method. Finally, the insulation is optimized by adding an electrostatic screen and increasing the insulation distance of the first end of C section winding, and the overload capacity is optimized by increasing the wire diameter of high-voltage winding, the cross-sectional area of the core, and the number of turns of winding. The heat dissipation is optimized by increasing the heat transfer coefficient of the side surface so that the function of increasing the insulation strength, improving the overload capacity and reducing the temperature rise can be realized, and the finite element simulation analysis is carried out. The simulation results show that the maximum field strength of the optimized grid potential transformer is reduced from 2.79 kV/mm to 2.24 kV/mm, which increases the end insulation margin; the saturation degree can be controlled within 110% under 90 kV frequency withstand voltage, and the excitation current can be within the limit capacity, which effectively improves the overload capacity; the hot spot temperature is re-duced from 115.7 ℃ to 108.8 ℃, and the heat dissipation capacity is improved. The simulation results confirm the rationality of the optimized design and provide some reference for engineering applications.