In order to research the characteristics of the transmission gear rattle, a special test transmission containing only two stalls was designed. The test transmission considered the complex relationship between each part, internal dynamic excitation of gears, engine speed fluctuation and load incentives, bearing stiffness and damping characteristics, and flexible properties box. A transmission rigid-flexible coupling multi-body dynamics model was built in LMS virtual lab software. The condition of transmission gear system rattle was introduced, and an accurate expression of rattle time history and each factor was derived. Finally, each rattle factor was analyzed systematically based on the rigid-flexible coupling model. The results showed that the rattle can be controlled in the ideal range through rational design of the gear system parameters.