A power flow analysis based on a substructure approach is performed to exhibit vibration transmission in a complex coupled beam-cylindrical shell system. The system is divided into a shell substructure and a beam substructure, which are coupled by three spring-dampers. The theoretical receptance function of each substructure with a free-free interface condition is formulated by modal analysis to describe the dynamical behavior. On the basis of the receptance functions of the two substructures as well as synthesis through the geometrical compatibility and force balance conditions at the coupling interfaces, the dynamic characteristics of the coupled system are calculated. Both the input and transmitted powers within the system are estimated, and the influences of the excitation locations, the stiffness and loss factor of the spring-dampers on the vibration transmission are investigated as well.