According to the principle of main circuit for centralized power EMUs in China, the high voltage electrical box equipped with two main circuit breakers was researched and designed, which not only optimized the arrangement of roof equipments, but also improved the operating environment, improved the safety and reliability of high voltage equipments. With the consideration of the arrangement for high-voltage equipments and the requirements of structural design, the simulating calculation for the electrostatic fi eld and transient electric fi eld was carried out to get the distribution rule for the electric potential and electric fi eld. According to the results of electric fi eld simulation, the optimization methods for electrostatic fi eld of high voltage electrical box were obtained.