Using the discrete element method (DEM), this study derived the optimal shape ratio of a grouser driving in a coastal terrain. To develop a DEM model that considers the properties of the coastal terrain, experiments were performed on the physical and mechanical properties of the terrain, and parameters of the DEM model were calibrated using the experimental results. In addition, a terramechanical experiment was performed to validate the DEM model, for which parameters were calibrated. Furthermore, simulations were performed on the change in thrust according to the existence or nonexistence of the grouser and the change in thrust and sinkage according to the shape ratio using the validated DEM model. Consequently, the track with grouser generated a larger thrust than that without the grouser. Thus, the optimal shape ratio range of coastal terrain was derived using the DEM model, considering the mechanical properties of the terrain.