In order to protect the high-voltage electrical equipment on the roof of Fuxing EMUs from the influence of external harsh environment and ensure the good working performance of the equipment, the high-voltage electrical box on the roof of EMUs was developed, and the components such as vacuum circuit breaker, high-voltage grounding switch, high-voltage disconnector,lightning arrester and transformer were integrated. According to the use conditions of high-voltage electrical box, the insulation performance analysis was carried out to determine the basic insulation capacity parameters of high-voltage electrical box; based on the design method of gas-solid composite insulation, the insulation top cover and insulation partition were designed to solve the problem of insufficient insulation in the height direction of the box; through the strength simulation calculation of high-voltage electrical box, the stress situation and safety factor of high-voltage electrical box under 7 different working conditions was calculated. Through the insulation performance test and impact vibration test, the insulation performance and structural strength of the prototype were tested and verified. The test results showed that the high-voltage electrical box could meet the requirements of insulation design, structural strength and EMUs operation.