Abstract: Based on an analysis of wind turbine off-grid accidents,a systematic testing scheme of harmonic resonance is proposed.The harmonics level and characteristic on different test points are researched,including point of connection of wind farm and a 35 kV bus of power collecting line and wind turbine.The mechanism of wind turbine harmonic resonance is analysed and found to be caused by the leakage inductance of wind turbine transformer and filtering capacitance of wind turbine converter on the grid-side.And the calculated result of resonance frequency at the resonance point is 1.1kHz.In the end,apractical harmonic elimination scheme is put forward,which is proved effective by simulation results and field tests.