Twin-screw compressors are used in many different industries that demand high-performance and low-noise and high-efficiency energy systems. Predicting the dynamic responses of a twin-screw compressor with gas-induced cyclic loads is necessary to improve the transmission characteristics of compressor systems and to reduce the vibration and noise of those compressor systems. This paper proposes a new method to predict the dynamic response of a multi-body model of a screw-rotor and bearing system by comparing and evaluating the results obtained from experimental measurement and a simulation program. The fluctuating torque and forces that are induced by cyclic gas pressure are applied to the screw rotors of an oil-injected twin-screw compressor. Three different cases are presented to illustrate and verify the merits of the proposed method. The stimulated vibration frequencies of the proposed model fit well with those measured vibration frequencies of the experimental model.