Abstract: For the characteristics of 660 VAC voltage in a coal mine, we study the reactive compensation principle of mining flameproof static var generator which takes NPC multi-level structure as main topology. On this basis, we analyze the phenomenon that the time delay of control closed loop caused by filter and digital processor affects its power in controller design. Through the comparison with model compensation method in time delay, we propose the method of reducing reactive power by current loop compensation. Experiment results demonstrate that the unit power factor is guaranteed with better compensation effect by current loop compensation.