In this paper, simulation and analysis of thin steel cylindrical shells of various lengths and diameters and thickness with triangular cutouts have been studied. In this research buckling and post-buckling analyses were carried out using the finite element method by ABAQUS software. Moreover, the effect of cutout position and the length-to-diameter (L/D) and diameter-to-thickness (D/t) ratios on the buckling and post-buckling behavior of cylindrical shells have been investigated. In this work the cylindrical shells used for this study were made of mild steel and their mechanical properties were determined using servo hydraulic machine. Then buckling tests were performed using a servo hydraulic machine. In order to numerical analyze the buckling subject to axial load similar to what was done in the experiments; a displacement was applied to the center of the upper of the specimens. The results of experimental tests were compared to the results of the finite element method. A very good correlation was observed between numerical simulation and experimental result.