Abstract: The electromagnetic excited harmonic response analysis of semi-direct drive wind turbine is very difficult due to its multi-disciplinary coupling and complex modeling. In this paper, a complete set of methods are formed through the design and research of the medium speed permanent magnet wind turbine with large megawatt grade, such as analysis and extraction of electromagnetic excitation load, simplification and establishment of elector-mechanical coupling analysis model, harmonic response analysis, real machine test and comparison, which systematically solves the difficult problem of electromagnetic excitation harmonic response analysis.