In this study, numerical study on the wind tower sections and tower flanges of wind turbine with dynamic load applied was conducted using the fluid-structure interaction (FSI) analysis. The lengths of tower sections (L1, L2) were applied as the design parameters to derive optimal design of the wind turbine. The structural stability of the wind turbine was evaluated by von Mises stress distributions. The results were described graphically, and the optimal configurations of tower sections and flanges that can endure harsh dynamic load conditions were deducted.