The bending vibration of transmission shafting directly influences dynamic performance of mechanical systems. The adoption of carbon fiber-reinforced plastics (CFRP) hollow shaft in the long-span transmission shafting can effectively reduce bending vibration. This paper aims to modify the transfer matrix method (TMM) for the CFRP/Steel composite transmission shafting system based on lamination theory and layer-wise beam theory. The dynamic kinetic equations of the steel and CFRP segments of the composite transmission shafting were modeled; then the bending vibration was solved by combining the boundary conditions of the CFRP/Steel composite transmission shafting. The experimental tests have been carried out in the CFRP/Steel composite transmission shafting to obtain the critical speed of rotation. Moreover, the results of modified TMM were compared with experimental tests, finite element method, and simply supported beam model. The comparison results show that the modified TMM proposed in this paper can effectively calculate the bending vibration characteristics of the CFRP/Steel composite transmission shafting system.