This paper presents the design optimization of filament winding composite cylindrical shell under hydrostatic pressure to maximize the critical buckling pressure. To this end, an optimization framework has been developed by employing numerical solution integrated with genetic algorithm. The design variables are fiber orientation and the corresponding number of layers. The framework is used to find the optimal design of filament winding composite cylindrical shell subjected to hydrostatic pressure. Three types of winding pattern are investigated, and the maximum critical buckling loads are increased by 26.14%, 25.82% and 20.95% compared with the base line, respectively. The influences of design variables on the critical buckling pressure are investigated. Results show that filament winding angles have more significant effect on the critical buckling pressure than the corresponding number of layers. Comparative study is carried out to verify the efficiency and accuracy of the optimization framework. Compared with the finite element analysis, the optimization framework has significant advantages in terms of calculation efficiency.