Abstract: In this paper， the strength and ultimate carrying capacity of cylindrical shells with assembly-type ribs and with flat ribs are calculated respectively using the finite element method. The difference in strength between these two types of shells is studied. The stress responses at three typical positions on the shell with assembly-type ribs are calculated for different loads， and the effect of the assembly gap on the ultimate carrying capacity is also analyzed. Then， for the cylindrical shell with flat ribs， the difference of strength and ultimate carrying capacity results by using different modeling methods are investigated. Simulation results show that the non-linearity relationship between the pressure and stress can be clearly observed for the cylindrical shell with assembly-type ribs； specifically， the smaller the assembly gap is， the larger the ultimate carrying capacity becomes. Meanwhile， for cylindrical shells with flat ribs， the effect of computational modeling on strength， either being Solid elements only or the combination of Sshell and Beam elements， is quite obvious， while that on the ultimate carrying capacity is negligible.