Abstract: A nonlinear simple single stage planetary gears dynamic model that contained multiple backlashes and multiple time-varying parameters was established, wherein the backlash, time-varying mesh stiffness and its engaging phase difference, gear mesh composite errors and time-varying planet position angle were considered. According to different input rotational speed and torque, operational terms were categorized into four work conditions. The vibration behaviors were described in detail by frequency spectrum, dynamic load coefficient and load sharing coefficient. The results demonstrate that the changes of nonlinear vibration behaviors represent diverse characteristics in different work conditions. The change of nonlinear behavior that is generated by ascending rotational speed worsens vibration more clearly in light load condition than heavy load condition. At the same time, the change that is brought by increased load improves vibration more obviously in high speed state than low speed state. The change of nonlinear behavior is staged similar in frequency spectrum, each vibration characteristic parameters also have staged similar character that is consistent with frequency spectrum. It provides reference for the design of planetary gears in complicated work conditions.