Abstract: Objectives In order to improve the mechanical properties and lightweight level of ultra-long pressure-resistant ring-stiffened cylindrical shell structures and solve the problem of optimized design of ring-stiffened cylindrical shells under large length-to-diameter ratios. Methods The mechanical properties of reinforced cylindrical shells under different length-to-diameter ratios were analyzed by combining theory with the finite element method. The equal stiffness cylindrical shell is optimized and designed through the optimization algorithm, and a reasonable adjustment strategy for the characteristic stress limit value is proposed. Based on the optimization scheme of the equal stiffness cylindrical shell, the variable stiffness cylindrical shell with length-to-diameter ratio of 5 is designed and regarded as the basic unit. A design method of the ultra-long reinforced cylindrical shell based on the variable stiffness basic unit is proposed. Results The constructed design scheme of the ultra-long ring-stiffened cylindrical shell has an average overall weight reduction of 1.07% compared with the equal-stiffness lightweight scheme, while the critical pressure for global instability has increased by 1.49% on average. Conclusions The proposed construction method based on variable stiffness basic unit is simple and fast, providing a useful reference for the lightweight design of ultra-long ring-stiffened cylindrical shell structures.