In order to investigate the vibration noise of multi-stage planetary gearbox under complex excitation before and after tooth modification, with taking the lifting gearbox of an offshore platform as the research object, a finite element model of the gearbox including coupling four-stage planetary gear train, bearings and housing is established, and vibration mode of the gearbox is analyzed. Internal dynamic excitations of gear pairs before and after tooth modification are solved by static and dynamic contact finite element methods, then a vibration noise prediction method considering tooth modification is developed, vibration responses of the gearbox before and after tooth modification are solved by mode superposition method, and accordingly radiation noise of the gearbox is predicted by acoustic boundary element method. The results show that the vibration noise of the four-stage planetary gearbox after modification are decreased apparently, and calculated vibration noise is in good agreement with experimental values.