The gearbox housing is the most complex structure in transmission,which suffered multi-source dynamic excitation. The damage of dynamic load is much greater than static load. The rigid- flexible coupling multi- body dynamics model of the gear transmission system is built,the dynamic force response of bearing seat and the dynamic force of the point of suspension under the random road excitation spectrum under the gear time- varying stiffness,damping,meshing error and the torque ripple of the ISG is solved. On this basis,the dynamic response analysis of housing is carried out by using a mode superposition method. The results show that,the overall design is more conservative relatively,but the middle of the plate- type parts have large deformation,smaller stiffness and need to focus on early in the design.