In traditional design of wind turbine transmission systems, the gearbox and generator are designed independently. This method ignored the coupling constraint relationship between the gear system and the generator system, which greatly affects the power density improvement and dynamic performance optimization of the transmission system. This paper proposes a multi-level coupling integrated design method for gearbox-generator system parameters of wind turbine transmission system. This integrated design method gradually achieves global optimization to local optimization, combining static performance optimization with dynamic performance optimization. In the first level, the finite element method and numerical calculation method are used to design the initial parameters of the gearbox-generator system to improve the power density of the gearbox-generator and reduce the peak value of internal excitation. Taking the results of the first level as the initial parameters of the second level, based on the electromechanical coupling dynamic model of the gearbox-generator, the correlation between the mechanical structure parameters of the gearbox and the generator and the electromechanical coupling dynamic characteristics of the system is studied. The proxy model of dynamic characteristic is established, and the optimization of bearing, hollow shaft size, spline size, stiffness of internal gear ring connection bolt and structural parameters of generator is completed. Finally, the vibration reduction and load reduction effects of the original scheme and the optimized scheme of the transmission system are analyzed under rated and various power generation operating conditions.