Abstract: The mode synthesis is combined with the finite element method to analyze the vibration characteristics of the rotor-bearing-case system of an engine. The generalized state space mode synthesis method is adopted to calculate the coupling vibration characteristics between the axisymmetrical rotor and the case, and the complex mode synthesis method is applied to calculating those between the non-axisymmetrical rotor and the case. The finite element method is used to analyze the substructures.A program, named AROBEC, has been written for this purpose. It can calculatethe whirl frequence, critical speed, stability, unbalance response and transientresponse for engine system. The program includes preprocessing and postprocessingfunctions and provides conical shell finite elements and rotor finite elementswith viscous damping which take shear effect into account. The dynamic characteristics of three types of aeroengine have been analyzed with this program and the results are satisfactory.