For the safety of maintenance personnel of electric locomotive, a high voltage protection alarm system is designed based on STC11F04E microcontroller. The system consists of high voltage induction part, signal processing module, voice alarm module and power management module, etc. The system can detect the high voltage electric field of locomotive roof and convert it into voltage signal, and through the measurement of signal processing module, decides whether an alarm should be given. This system has been qualified through several testing authority and put into use.