Abstract: Part of hoist system in coal mine adopt full digital DC motor speed control devices, which easily brings about harmonic wave and pollutes the coal mine grid. In order to solve this problem in the coal mine, four-wire system based on three-level four-leg topological structure is developed in this paper. The frequency dividing control algorithm is studied and Emphasis on specify the harmonic current compensation control technology. At last, It gives the specified harmonic current compensation control method for three-level four-leg through MATLAB simulation, and verify the control method through the experiment.