A nonlinear,torsional dynamics model of a two-stage planetary gear train with time varying meshing stiffness,errors of transmission and backlashes was established. The dimensionless equations in generalized coordinates of the system were derived and solved by using the method of numerical integration. The influences of excitation frequency and damping coefficient on the bifurcation and chaos properties of the system were analyzed by using bifurcation diagram,phase trajectory and Poincáre section. The paper ...