Abstract: The ring-stiffened cylindrical shell is the most widely used pressure structure in underwater engineering products. The traditional stress analysis method of ring-stiffened cylindrical shell under hydrostatic pressure is to simplify the cylindrical shell as a bending beam in bidirectional stress state. With the emergence of new design features such as large depth loads and large thickness in deep-sea pressure structure, the assumption of bidirectional stress state for cylindrical shell becomes unreasonable. This paper proposed a simplified mechanical model for ring-stiffened cylindrical shell, which transforming the stress problem of ring-stiffened cylindrical shell under hydrostatic pressure to the superposition of bending beam stress under axial force and plane annulus stress under radial force, and thereby a three dimensional stress analysis method of ring-stiffened cylindrical shell has been derived. The calculation results of the example show that the proposed method is in good agreement with the finite element simulation results of the ring-stiffened cylindrical shell with new structural design features. Compared with traditional stress analysis methods, the proposed method has better calculation accuracy and relatively safer calculation results. At the same time, it is found that the stress characteristics of the ring-stiffened cylindrical shell under the new structural design features are significantly different from those of the traditional thin cylindrical shell.