Abstract: Because the capacitive effect of power cables at the same voltage level is over 20 times larger than that of overhead lines,the harmonic resonance amplification problem which is not serious in the onshore wind farm integration may become very serious in the offshore wind farm integration. To this end, this paper studies the harmonic resonance amplification problem caused by the offshore wind farm integration and its mitigation principle. Firstly, the harmonic resonance amplification mechanism caused by offshore wind farm integration is analyzed, and the technical path of mitigation is given in principle. Then, taking a real offshore wind power integration project as a study case, the harmonic models of the offshore wind power grid and the onshore power grid are established, respectively, including the harmonic models of cables, transformers and wind turbines, the equivalent harmonic models of the extra-high voltage（EHV） large-scale grid and the low-voltage distribution network. According to the established harmonic models, the causes of harmonic resonance amplification are analyzed, and a mitigation scheme for solving the problem of harmonic resonance amplification is proposed and verified. Finally, the mechanism and mitigation principle of harmonic resonance amplification caused by offshore wind farm integration are summarized.