Based on the dynamic theory of multi-body system, a multi-rigid-body dynamic model, which contains the transmission system and structure system of marine gear device, was established by taking account of the internal excitations such as the time-varying mesh stiffness, tooth backlash and bearing stiffness and the external torque excitation caused by the propeller. Then, the dynamic meshing forces of gear pairs and bearing reaction forces were calculated. Using the modal superposition method, the dynamic response of housing surface was solved after the multi-flexible-body dynamic model was developed on the basis of the flexible gearbox and pedestal. Afterwards, a strongly vibro-acoustic coupled model of this gearbox was built by employing the frequency histories of bearing reaction forces obtained from the multi-body dynamics analysis, and the surface sound pressure of gearbox and the radiation noise of outer sound field were calculated. The results show that the peaks of dynamic meshing forces, reaction forces of bearings and dynamic responses of gearbox appear at the position of mesh frequency and its multiples of gear pairs, and the simulation results of vibration acceleration of gearbox and the radiation noise of outer sound field are in good agreement with the experiment results measured in the vibration and noise test platform of the gearbox.