Abstract: For problems of poor filtering effect and easily leading to resonance overvoltage and harmonic amplification of existing passive filter, the paper proposed a new method of harmonic elimination based on fundamental resonance principle. The method seriesly connects a fundamental resonant circuit composed by inductance and capacitance in three-phase line between electricity grid and passive filter, so as to force harmonic currents to flow into passive filter and significantly enhance efficiency of the filter. The experimental result shows that the current distortion rate drops from 10.6% to 0.942% after adding fundamental resonant circuit, which indicates the new method has better filter effect.