The traditional research on the dynamics of planetary gear transmission system is based on the assumption that the support is on the ground. However, the planetary gear transmission system inside the aircraft is spatially moved along with the airframe, which is not only subject to gravity, but also to convected inertia force and Coriolis inertia force, as well as gyroscopic moment. These loads affect the dynamic characteristics of the planetary gear transmission system. In order to investigate the dynamic behavior of planetary gear transmission system in non-inertial system of aerospace environment, the kinematic equations of the central component and planetary gear in arbitrary spatial motion state of the airframe are deduced with the influence of internal non-inertial system and external non-inertial system. Subsequently, the coupling dynamic model of planetary gear transmission system is established, which is in non-inertial system of aerospace environment. The motion variation law of planetary gear transmission system in the non-inertial system and the dynamic behavior of each component in different non-inertial conditions are researched based on the hovering motion of the airframe. The results indicate that the radial equilibrium position of the planetary gear has great offset due to the influence of non-inertial system inside the planetary gear train when the airframe has no spatial motion. Moreover, the gravity on each component will generate radial force, which and additional inertial force will vary with the external non-inertia conditions when the airframe is in the state of spatial motion. In addition, different non-inertial conditions have significant influence on the motion trajectory, bearing force and acceleration of each component, and have different influence rules on the central component and planetary gear.