This research aims to perform the optimal design of filament wound type 3 tanks under internal pressure. So far, most designs have not been optimized to account for the requirements of filament wound structures, and no design method exists for general filament wound structures under internal pressure, satisfying given design requirements. In this research, a new design algorithm which had been proposed in our previous research was utilized. The optimal design algorithm includes the semi-geodesic path algorithm, progressive failure analysis and genetic algorithms. In addition, a modified sub-string genetic operator that improves the genetic algorithm was newly suggested and verified through a basic design. Finally, the optimal design algorithm was applied to a representative filament wound type 3 tank-high pressure hydrogen storage tank.