A 3-D finite element model was established for the dual-rotor model including complicated geometries. By utilizing Craig-Bampton mode synthesis method

the model order reduction was carried out. Through comparative analyses in critical speed and eigen problems

the validity and efficiency of the reduced order model were verified. On this basis

the critical speed map and the value of critical speed under a constant ratio were calculated. Results showed that the high-dimensional solid finite model was successfully reduced to a lower one with only a few dozen degree of freedom (34 DOFs) by means of Craig-Bampton method

and the maximum error of the first two orders critical speed and the first six orders eigen value were kept less than 0.43%. Based on analysis of the framework in which the model is created by reducing the two single rotor subsystems and combining them under compatibility condition

dynamical problems such as critical speed can be easily solved.