Abstract: To evaluate the contact fatigue life of the gear transmission system,the gear transmission system of the 2 MW wind turbine was studied. The random wind speed model was established by introducing the wind speed variation law and using the Weibull distribution. Considering the external wind load and the internal load excitation caused by gear and bearing stiffness,the translationtorsional dynamic model of the planetary gear transmission system was established. The dynamic meshing force and the corresponding stress of each gear pair of the transmission system was calculated. According to the characteristics of gear transmission strength and randomness of load,the fatigue effect was characterized by strength degradation of gear teeth,and the residual strength model was established based on nonlinear fatigue damage accumulation theory. On the basis of traditional stress-strength interference theory,the dynamic reliability function of gear transmission system under random wind load was obtained. The dynamic reliability curve of parts was described by perturbation method. The results show that:under the combined action of strength degradation and random load,the fatigue reliability of each gear of wind turbine system gradually decreases with the service time,and the reliability decreases rapidly in the early stage of service,and gradually slows down in the middle and later stages of service. The strength degradation form and load size affect the trend of the reliability. The model reflects the variation of the reliability of the gear transmission system with the service time,and provides a reference for the reliability design and fatigue life prediction of products.