The planetary bearing is an indispensable component of the planetary transmission mechanism. The contact characteristics between the rollers and raceways have a great impact on the mechanical behavior of planetary gear train. The coupling dynamics modeling of planetary gears and bearings is challenging due to their complex structures. There is a lack of relevant research on the reliability issues of the planetary bearing in the context of speed increase and fluctuation in input power in electromechanical coupling transmission systems. To address this gap, a dynamic model of the planetary gear train is established considering the coupling effect including rotation and revolution in this study. The calculation method for the contact force and stress are proposed, and the contact characteristics under different conditions are obtained. Factors influencing dynamic load and contact stress are analyzed. The findings of this study can provide relevant references for improving the working life and reliability of the high-speed planetary bearing.