For the integrated structure of the wind power transmission system, an electromechanical rigid-flexible coupling dynamics model suitable for wind turbine generator under variable-speed and variable-load conditions was proposed. This model considered mechanical factors such as time-varying meshing stiffness of gears, phase relationship, and structural flexibility of the shaft and shell, as well as electromagnetic factors such as saturation characteristics of permanent magnet, radial force wave and space harmonic wave. The electromechanical coupling dynamic characteristics of the gearbox-generator integrated system were investigated, and the influence of the flexibility of the housing on the dynamic characteristics of the system was discussed. An acceleration analysis method was introduced to identify the resonance speed of the system. By using the modal energy method and the formation vector distribution principle, potential dangerous components in resonance were identified. The results show strong coupling between the gear system and the generator. The flexibility of the housing has a significant effect on the electromechanical coupling characteristics of the system. For the integrated system, internal gear excitation is the main excitation source at the resonant speed. However, when a thin-wall housing is used, electromagnetic excitation from the generator cannot be ignored, making it easy to stimulate new resonance speeds. Selecting a reasonable thickness can effectively improve the safety and reliability of the system, reduce the resonance area and mitigate damage to system components.