To evaluate the destruction of structures by tsunami forces, it is desirable to correctly evaluate not only the sustained forces due to the water level but also the impact forces generated at the tsunami front. To this end, it is necessary to conduct numerical simulations based on the three-dimensional Navier–Stokes equations, but the validity of the calculation results is not guaranteed. Therefore, this study compares the results obtained blind before confirming the experimental results and the results obtained by adjusting the parameters after confirming the experimental results. Recommendations are made to resolve issues that arise.