Abstract: This paper summarized the basic mathematical method used in the Aeronautical Structural Analysis System HAJIF--I-the supermatrix method and itsapplication in analysis of multi-substructures.Supermatrix method is powerful for the processing of large sparse matrix. This method is adaptable and versatile to the third and fourth generations of computers. The multi-substructure static analysis system established in the HAJIF-I by supermatrix method is applicable not only to the analysis of simple structures, but also to the analysis of complicated structure, and especially with superiority to large complicated problems.Emphasis of this paper placed on the multi-level supermatrix and theiralgorithms, and complicated aircraft structure analysis-application of theHAJIF-I. Finally large complicated numerical example has shown good adaptability and efficiency of this method. ,