The transmission characteristics of the precision RV reducer is mainly determined by the mesh state between the cycloid gear and pin shell parts,and vibration modal characteristics of the cycloid gear have important effects on the dynamic characteristics of the whole reducer. Based on the 3 D model of the RV reducer,the vibration modal characteristics of the cycloid gear considering three states,namely the free,bearing support and mesh states,are obtained using the finite element method.Simulation results show that the modal characteristics of the cycloid gear in the meshing state matches better with the working mode of the RV reducer than the other states,The natural frequencies the cycloid gear increase remarkably,and the vibration modes are changed accordingly. These works are useful for the analysis on the dynamic transmission characteristics of the RV reducer.