This paper attempts to improve the efficiency in analyzing a composite beam with variable crosssection and reduces the computation time.Considering the adyantages of few calculation burden and high efficiency,the differential transformation method (DTM)was applied to study the impacts of various parmeters on the dynamic characteristic of the composite beam with internal damping.The results show that the modal frequency of composite structures will decrease when the length of the beam and the amount of the Young module increase,as well as the thickness of the base layer decreases;the modal loss factor of composite structures will increase when the thickness of the damping layer and the height of the base beam are both reduced,as well as the value of the Young module and loss factor in the damping layer increases.