Abstract: The dynamic analysis based on the complete finite element model is computation intensive, time consuming, and inefficient. Therefore, the modal synthesis technology based on substructures serves a realistic basis of application. This paper studies the effectiveness of the fixed-interface modal synthesis method for the dynamic analysis of complex spatial structures, and develops a software for the dynamics analysis of a large space combination. The dynamic analysis of a three-cabin combination of the space station is carried out to verify the effectiveness of the fixed-interface modal synthesis method for large-scale finite element model. It is demonstrated that the method is applicable under complex interface conditions, and that it can be applied in the actual engineering.