Abstract: Based on the semi-analytical solution of Hamilton canonical equation, a new mathematical model for the vibration characteristics of a group of double-shell structures is proposed. The basic steps are as follows: 1. the linear equations of inner shell, outer shell and stiffeners are established independently; 2. the compatibility conditions of displacements and stresses on the interfaces between the shells and the stiffeners are employed to derive the governing equations of the whole structure. The presented method possesses following advantages: i)the same Hamitonian isoparametric element can be used to discretize both shells and stiffeners; ii)the transverse shear deformation, the rotary inertia of the structure are all taken into consideration, furthermore, no limitations exist in the thickness of shell and the height of stiffener; iii)similar to finite element method, it can handle the cases of complex boundary conditions and multi-material compositions. The proposed method can also be easily generalized to solve the dynamics problems of stiffened composite laminated shells/double-shell structures, and stiffened piezolaminated shell/double-shell structures.