Abstract: In this paper, the critical hydraulic pressure of the overall instability of ring-stiffened pressure vessels in submarine is obtained under the hypothesis of structural orthotropy. The finite element analysis software ALGOR is used to verify the results. Critical pressures of the cylindrical Shells stiffened by rings with semi-torus section and by circular tube are calculated and compared. The results show that the performance on resisting the hydraulic pressure of the cylindrical shell stiffened by rings with semi-torus cross-section is better than the latter if they have the equal weight of same material. It is also found that the critical hydraulic pressure decreases with the increase of the oblique angle of the rings