Abstract: The finite element solid model of transmission was established by using the mixed finite element method of three-dimensional solid, spring-damper and coupling matrix elements, and the modal analysis of the transmission drive system and assembly was done below the third gear. The dynamic responses of the gear transmission system were computed under gear tooth time-varying stiffness, impact and manufacturing error excitations. The results showed that the transmission did not produce resonances under the specific condition of the third gear. There were many frequency components, such as fractional, double and modulation frequencies. The vibration responses displayed multi-period nonlinear characteristics. The research results may make a good foundation for the noise analysis and optimum design of the transmission.