Abstract: HAJIF-II is a program system developed by Chinese Aeronautical Establishment（CAE）. It is able to accomplish the calculation of the modal characteristics of aircraft structures as well as the flutter and gust response analysis with the active control system taken into account. The structural model may be composed of 99 substructures each with 7000 degrees of freedom. 300 panels may be used in the calculation of nonsteady aerodynamic forces and 50 modes in the flutter and gust response analysis. The data generation system permits the flexible use of numerical data and topological description. 31 prescribed computational flows are supplied and an user can also organize his own computational flows as he needs. A structure can be discretized into finite elements or simulated by single spar. For the management of the stiffness and mass matrix a modified hypermatrix method is employed to omit all of inactive zero elements more effectively. A new algorithm, called a revised simultaneous iteration procedure, has been developed to solve the real eigenvalue problem and is more effective than the current agorithm. Modal synthesis technique with both free and fixed interfaces is adopted. Besides, two new methods of synthesis have been developed from the concept of multilevel substructures. Nonsteady aerodynamic forces are calculated by means of subsonic doublet lattice method for multiwings and aerodynamic forces in Laplace plane can be approximated with a curve-fitting procedure based on sinusoidal data. Flutter equations are solved by V-g and p-k methods and the continuous atmosphere turbulance are used in the gust response analysis. The system consists of a sequence of functional modules so it can be modified and extended easily. An advanced file management system has also been developed. There are approximately 26000 FORTRAN IV statements in the system. The HAJIF-II was applied to analyzing a number of typical aircraft structures and gave good results.