To study the testing methods and issue diagnosis of high-voltage systems in new energy vehicles, this paper examines high-voltage electrical safety from two levels: equipment-level and vehicle-level and analyzes existing the high-voltage electrical safety regulations, standards, and the current technological status of new energy vehicles. The study also investigates the high-voltage insulation condition of new energy vehicles and corresponding protective measures, including the principles and testing methods of high-voltage insulation systems and monitoring systems. Finally, comprehensive solution for high-voltage electrical safety analysis, protection, design, and testing has been developed. This solution can perform exhaustive verification across various operating scenarios of new energy vehicles, enabling precise identification of system safety threshold violations and validation of operational safety, thereby simplifying the difficulty of issue diagnosis.