This paper presents a dynamic finite element analysis model for a wind turbine gearbox in which a number of internal gears mesh with each other in a complex pattern. Differing from the conventional dynamic models in which the detailed gear teeth are fully modeled or gears and shafts are replaced with lumped masses, the tooth contact between a pair of gears is modeled using a spring element. The equivalent spring constant is determined by computing the stiffness of a gear tooth using a finite element analysis. The numerical accuracy of the proposed dynamic model is verified through a benchmark experiment of a gearbox with simple gear transmission system. In addition, the natural frequencies and dynamic responses of a 5 MW wind turbine gearbox that are obtained by the proposed modeling technique are given to support its validity and effectiveness.