In this research, the Abaqus finite element simulation software was adopted to calculate and analyze the critical height of the section rib-ring in supporting the sandwich composite pressure shell. First, the simulation method was verified by comparing the simulated result with related experimental results. Then three series of T section rib structure models were established in different layer methods and different sizes to calculate their capability to support sandwich composite pressure shell long cabin section. The buckling loads of these models were carried out and the conclusions are drawn as follows. By setting rib-ring, the stability of the long section pressure shell can be effectively increased. When the rib-ring support stiffness increased to a certain value, the overall buckling mode of the long section would be limited by the connection section with the rib-ring as boundary and turn into several single section buckling modes. The certain value of the rib-ring height is called critical height, and the calculation method is given in this paper. When the rib-ring support stiffness is greater than the critical stiffness, the critical buckling load of the structure has little relation to the properties of the rib-ring, while it is related to the size and material properties of the sandwich cylindrical shell. This critical buckling load of the structure is called section buckling load, which can reach 7.0 MPa for the sandwich composite pressure shell structure analyzed in this paper.