The analysis of structures may be classified into three categories: theoretical, numerical, and experimental approaches. The numerical and experimental methods are very useful when the structures to be analyzed have complicated shapes or geometry because theoretical methods are restricted to simple and special cases. However, the theoretical methods are very important analysis in the viewpoint that they can give basic insight for the structural behavior. Among them the modal model method is widely used because of the powerful propertiy of eigenfunctions(mode shapes), or orthogonality. In this paper, the modal model method was reviewed and studied for various models for structures: string, beam, membrane, and plate. Governing equations and solution methods were compared and a structural-acoustic coupling system was used for an application.