Abstract: Due to the complex operating conditions of the Yunnan-Guizhou Plateau and the China-Laos cross-border railway lines, locomotive electrical protections are frequently triggered. However, traditional routine tests cannot achieve protection threshold detection under abnormal operating conditions, posing potential safety hazards. This paper develops a novel protection function testing device for locomotive microcomputer systems. Incorporating core technologies such as partitioned modular architecture, multi-channel programmable constant-current source simulation, low-voltage safety testing, and automated protection logic verification, the device can effectively simulate various fault conditions including overvoltage, undervoltage, overcurrent, short circuit, grounding, and overtemperature. Consequently, it achieves full-process safety detection of microcomputer protection thresholds, command outputs, and actuator operations. The developed device breaks through the limitations of conventional testing methods, enhances the independent maintenance capability for core locomotive components, and provides a solid technical guarantee for the safe and stable operation of locomotive fleets on plateau railways.