In order to improve the accuracy of the attitude-orbit coupling control problem of spacecraft with flexible attachments, a study on dynamic modeling of flexible spacecraft is conducted. As a result, a high-precision dynamic model based on the floating centroid frame system(FCFS) which can describe the attitude movement of spacecraft as well as the coupling relationship between the attitude maneuvering and the orbit movement better than the old ones is proposed by using the method of Finite-element along with Newton mechanics.The simulation result demonstrates that the FCFS model fits the practical restraint well and thus is applicable. The dynamic influence on the spacecraft caused by the vibration of the flexible attachments during the attitude maneuvering procedure can be calculated accurately by using the FCFS model and so is the changing of dynamic factors, such as the the velocity and the displacement of the centroid.The research results can provide theoretical basis for attitude-orbit coupling control problem of flexible spacecraft and thus achieve the purpose of improving control accuracy.