In order to understand and predominated the inherent vibration characteristics of the engine better, the natural frequencies and vibration mode shapes of the dual-rotor system of Aero-engine are calculated based on the ANSYS program. Compared with the original calculation, the impact by change of stiffness in bearings on the dynamic properties of the whole system is analyzed. Integrated with the mechanical vibration theory, dynamics evaluations for the design are carried out. The results show that the computing speed of this method is fast and the eigenvalue and the eigenvector can be obtained with high precision and few input parameters.