As the motion state of a planetary gear reducer is easy to bifurcate when the transmitted power changes, a study on the bifurcation characteristics of a planetary gear train changing with the transmitted power is explored in this paper. The local bifurcation characteristics were studied with CPNF(continuous Poincaré-Newton-Floquet) method on the basis of the nonlinear torsional vibration model of 2K-H planetary gear train. As a comparison, the global bifurcation diagram changing with power was calculated by using the method of numerical integration. The comparison results reveal that a nonlinear planetary gear train with certain parameters may have several coexisting periodic trajectories, some of them may be stable and some may be unstable. As the power gradually increases in the range of 196~220 kW, the stable asymptotic stable periodic trajectory may change into chaos in the way of inverse period doubling bifurcation. And chaos is easy to appear when the planetary gear train is under light load condition.