Abstract: For a thin thickness cylinder cabin under external pressure, it is essential in the normal condition to ensure the components of the cabin having enough strength and stiffness. The components under the normal pressure will yield if no enough strength and they will buckle if no enough stiffness. The critical lengths of the components decide their critical pressures when the components keep in original conditions. Therefore, it is right and necessary to research and to simulate strength and stiffness of the components first, and then to get the theoretical basis for engineering design.