In view of the problems of high risk of high voltage insulation failure, low control accuracy of battery management system (BMS) and poor efficiency of fault diagnosis in the electrical system of new energy vehicles under the conditions of rainy, high humidity and low temperature bumpy in Guizhou mountainous areas, combined with the needs of regional industrial development, the special design is carried out from the dimensions of weather resistance integration of high voltage electrical system, multi-condition adaptation of BMS, vehicle network and fault diagnosis optimization. Through the optimization of the IP67 seal structure of the high-voltage distribution box, the innovation of the BMS adaptive equalization control algorithm, the anti-interference design of the CAN FD bus, and the three-level verification system of "virtual simulation-real vehicle test-scene verification", the high-voltage fault rate of the electrical system is reduced from the traditional design of 0.8 times/km to 0.12 times/km, the equalization accuracy of the BMS cell is increased to ±5 mV, and the fault diagnosis time is shortened from 120 min to 42 min.