Abstract: In order to study the deformation of submarine pressure hulls under the effects of gravity, a sim-ple calculation formula of the deformation of the free ends of stiffened cylindrical shells is derived based on moment theory and non-moment theory, and the calculated results are compared with the results of Finite Element Analysis (FEA) which tests the reliability of the formula. The results show that when a thin-wall cylindrical shell simply supported at the bottom is affected by its own gravity, the deformation degree at the free end is directly proportional to the fourth power of the inner diameter of the cylindrical shell, and in-versely proportional to the square of the wall thickness; for cantilever cylindrical shells, the gravity load has little effect on the roundness of the free end plane. With the nonlinear increase of distance between the free end and fixed supporting end, the increase rate increases gradually. With the increase of the inner di-ameter of the cylindrical shell, the deformation degree of the free end decreases gradually. When the inner diameter of the cylindrical shell is 0.75 times its longitudinal length, the deformation degree of the free end is at a minimum, then increases gradually as the inner diameter increases. The gravity deformation calcula-tion of ring stiffened cylindrical shells in a horizontal state and the strengthening measures can provide ref-erences for further study.