With the development of new energy vehicles, the detection and fault diagnosis of high voltage system of new energy vehicles are becoming more and more important. The leakage of high-voltage system of new energy vehicles will lead to the failure of power on and normal operation of vehicles. At the same time, it is very important for the safety protection of the whole vehicle. Taking the leakage detection of byd-qin hybrid high-voltage system as an example, this paper analyzes the fault generation mechanism and puts forward the detection technology of new energy vehicles, so as to help maintenance personnel better grasp the diagnosis technology of new energy vehicles.