Abstract: Aiming at the reliability of wind turbine gearbox in service, this article takes the 2 MW fan gearbox as the research object, comprehensively considers internal excitations such as time-varying meshing stiffness and comprehensive error of the gear, establishes a dynamic model of the transmission system gear shaft bearing, and obtains the dynamic meshing force of each gear pair under constant load. The Weibull random wind speed based on the variation law of wind speed in the wind field is cited as the external excitation of the system, and the stress time history of each gear under variable load is obtained by combining external variable load and fixed load meshing force. According to the main failure modes of parts, the strength degradation process of parts is simulated by using Gamma stochastic process based on the traditional stress strength interference model, combined with the P-S-N curve value of gear materials.Considering the correlation between component failures, a functional function of the main failure modes of the system is established, and a hybrid Copula model is constructed to describe the correlation between component level and system level failures. The dynamic reliability of the gearbox system is obtained through multi-layer nesting. The results indicate that the fatigue failure of the gear tooth surface should be mainly considered in the early stage of fan service, and the bending fatigue failure of the tooth root mainly occurs in the middle and late stages of service; According to the system reliability curve, considering the failure correlation, results are more consistent with the actual working conditions. This provides a reference for the reliability design of fan gearboxes.