Efficient, precise dynamic analysis for a complex spacecraft has become a research focus in the field of spacecraft dynamics. In this paper, by combining discrete time transfer matrix method of multibody system and finite element method, the transfer equations and transfer matrices of typical elements of spacecrafts are developed, and a high-efficient dynamic modeling method is developed for high-speed computation of spacecraft dynamics. Compared with ordinary dynamic methods, the proposed method does not need the global dynamic equations of system and has the low order of system matrix, high computational efficiency. This method has more advantages for dynamic modeling and real-time control of complex spacecrafts. Formulations of the proposed method as well as a numerical example of a spacecraft with a flexible solar panel are given to validate the method.