As the power network appeared fault, the residual fault-current can be controlled under the allowed range by using the traditional Petersen-coil to compensate the most part of capacitive current. Although the small residual fault-current can also cause gas explosion in mining power supply system with high reliability. A novel control technology of neutral-point ground impedance is presented in the thesis by controlling the duty cycle of power electronics IGBT, The ground impedance control systems are with reactor continue changing, excellent dynamic responding, high control precision and the residual fault-current approaching zero, it can reduce the accident probability. Theoretical derivation and MATLAB simulation results show that the proposed method is with high precision, high speed and noiselessness. It can improve distribution automation, accelerate grounding fault arc self-extinguishing, and enhance power quality.