This paper regarded the threedimensionally carbon/silicon carbide braided composite as a spatial structure, which is made up of cellelements and contains matrix and fiber. The structure model of a cellelement for the threedimensionally multidirectionally braided composite was constituted geometrically and used for meshing the composite structure. Based on the cell model, we studied the dynamic behavior of the C/SiC composite cantilevered plate using finite element method. The theoretical dynamic behavior of the composite plate was also obtained and compared with the numerical result, which verified the correctness of the calculation model.