In order to avoid excessive vibration of the compressor rotor system during operation, it is necessary to carry out a systematic dynamic optimization design, including testing the vibration characteristics of compressor rotor and the whole machine as well as modeling and analysis based on rotor dynamics. In this paper, the rotor composite system (pump assembly and shell assembly) is taken as an example for the investigated subject. Firstly, a threedimensional solid finite element model of the compressor rotor system was proposed. The natural characteristics of the rotor system were analyzed through the numerical model, and five natural frequencies and mode shapes were obtained. Finally, the rationality of the analysis model was verified against the results of dynamical experiment. The study in this paper can provide essential technical support to reduce the vibration and noise of the compressor system.