The modeling method of forward recursive formulation of flexible multibody systems is used in this paper. Based on the principle of velocity variation, a rigidflexible coupling dynamics model of a spacecraft with Stewart platform, flexible solar panels and CMG components was established. Due to the large degree of freedom of the model, unable to meet the needs of realtime control. Therefore, an equivalent simplified model of the Stewart platform with simplified legs was established. Through comparison with the complete model of the flexible Stewart platform spacecraft, the correctness and efficiency of the established dynamic model were verified. The influence of the motion of the main platform and the vibration of the flexible panels board on the dynamic response of the payload is analyzed. It is pointed out that the motion of the main platform cannot be simply fixed or the vibration of the flexible panels cannot be ignored when designing the microvibration suppression scheme of the Stewart platform. The research in this paper provides effective technical support for microvibration damping and highprecision pointing of spacecraft with Stewart platform.