Abstract: During maintenance and repair work in power system operation, it is vital to keep certain distance between operation personnel and electrical power equipment, which is relying mainly on human observations unfortunately. Due to human errors such as misjudgment or negligence, equipment damage and human casualties may occur consequently. To meet the requirement of real-time safe working distance measurement, a distance measuring system based on high precision ultrasonic sensor, and using STM32 MCU as the core processor is designed for live working. Through wireless WiFi communications, the challenges of wiring with the device near high voltage charged equipment is solved successfully. Meanwhile this device is tested in Jingmen 1000 kV EHV Substation. The results show that the safety distance measuring system has effective safety protection functionality and it can timely alert the operator. It is of great significance for the safety of personnel and equipment.