The axial flux permanent magnet (AFPM) generator with double-sided internal stator structure is highly suitable for vertical axis wind turbines due to its high power density. The performance of the AFPM generator with double-sided internal stator structure can be improved by the reasonable design of electromagnetic parameters. To further improve the overall performance of the AFPM generator with double-sided internal stator structure, multivariable (coil width ωc, permanent magnet thickness h, pole arc coefficient αp and working air gap lg) and multi-objective (generator efficiency η, total harmonic distortion of the voltage THD and induced electromotive force amplitude EMF) functional relationships are innovatively established. Orthogonal analysis, mean analysis and variance analysis are performed on the influence parameters by combining the Taguchi method and response surface methodology to study the influence degrees of each influence parameter on the optimization objectives to determine the most appropriate electromagnetic parameters. The optimization results are verified by 3D finite element analysis. The optimized APFM generator with double-sided internal stator structure exhibits superior economy, stronger magnetic density, higher efficiency and improved power quality.