Abstract: With the increase of coal mine excavation distance, in order to meet the actual needs that the terminal voltage of the long-distance cable end motor in the coal mine is greater than 95% of the rated voltage when it is running and 75% of the rated voltage when it is starting, a mine flameproof mobile substation on load automatic voltage regulating device is developed. The device is mainly composed of step-down autotransformer, column-type stepless regulator, compensation transformer, mutual transformer and control center. This paper introduces the components of the device, the regulator brush control method and the voltage regulation strategy. The device collects the output line current and voltage synchronously, and can derive the motor end voltage with the special algorithm studied, and can realize automatic voltage regulation when there is a load according to the target value set by the user, so as to meet the voltage requirements for motor operation at the end of the cable.