A multi-rigid-body model which contains the structure system and transmission system of bridge crane gearbox is established with internal excitations such as the time-varying mesh stiffness, tooth backlash, bearing stiffness and damping and the external torque excitation caused by electric motor, and to calculate the dynamic mesh force of gears and the reaction force of bears. Then calculate the modes of the flexibility gearbox. Afterward, a vibro-acoustic coupling model of this gear system is built by taking the frequency histories of bearing reaction force as the boundary conditions, and the surface sound pressure and the radiation noise of outer sound field are calculated. The results show that the peaks of dynamic mesh force, reaction forces of bearings and dynamic responses of gearbox appear at the position of the frequency of shaft orders, mesh orders and its harmonic frequency; the maximum of radiated noise appear at 500Hz, where the surface sound pressure and the outer sound field are 82.9dB and 72.8dB.