The implicated motion of a ship during its voyage will have an important impact on the vibration of the marine mechani?cal system. Therefore，it is a significant practical work in engineering to study the dynamic characteristics and vibration control ofthe marine rotating machinery under the heave. This paper mainly discusses the nonlinear vibration mechanism and characteristics of the marine rotating machinery-air bag vibration isolation system under heave excitation. The mathematical model of the marine rotating machinery with air bag vibration isolation system is established，and the relationship between heave motion and rotor motion is analyzed by multi-scale method to reveal its vibration mechanism. The dynamic characteristics of the marine rotating machinery-air bag vibration isolation system under heave excitation are studied by numerical method，and compared with the approximate solution，the effectiveness of the theoretical results is verified.