Research on the problem of frequent failures of the potential transformer in the operation of the rolling stock, and 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 proves the correctness of the theoretical analysis 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, 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, and 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 2.79kV/mm to 2.24kV/mm, which increases the end in-sulation margin; the saturation degree can be controlled within 110% under 90kV frequency withstand voltage, and the excitation current can be within the limit capacity, which effectively improves the overload capacity; the hot spot temperature is reduced 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 a reference for engineering ap-plications.