Abstract: 【 Objective 】In order to explore the characteristics of optimization design schemes of titanium alloy double layer stiffened cylindrical shell structure under different length-to-diameter ratios and different water depths, 【 Methods 】In this paper, a mathematical model for lightweight optimization of titanium alloy double layer stiffened cylindrical shell structure was established, and the main control program of genetic algorithm was established based on Matlab. The ultimate bearing capacity was calculated and checked by the finite element software ANSYS. The differences of optimization schemes between titanium alloy single layer stiffened cylindrical shell and titanium alloy double layer stiffened cylindrical shell under different length-to-diameter ratios and different water depths were compared and analyzed. 【 Results 】There are two critical water depths in the optimization design of titanium alloy stiffened cylindrical shell, and the optimization design is divided into three optimization types: the stability constraint type of ultimate bearing capacity constraint control optimization design, the strength constraint type of strength constraint control optimization design and the joint constraint type of strength and ultimate bearing capacity constraint joint control optimization design. The larger the length-to-diameter ratio, the larger the critical water depth. Under the same water depth and length-to-diameter ratio, the weight of double layer shell optimization scheme is lighter than that of single layer shell, and the critical water depth of double layer shell optimization design is smaller than single layer shell under the same length-to-diameter ratio.【 Conclusions 】The research results can provide reference for the optimization design of titanium alloy double layer stiffened cylindrical shell structure.