Debris flows cause a lot of human and property damage in urban regions near mountainous areas, so it is essential to predict damage and prepare countermeasures. In this study, the applicability of the impact force of the debris flow acting on the check dam was reviewed using the calculation formula. Numerical simulations were conducted through the finite difference method according to changes in slope and flow velocity, and governing equations were used to satisfy the conservation laws of mass and momentum. In addition, the impact force of Austria, which is mountainous terrain, was calculated and analyzed. As a result of the numerical simulation, as the slope became steeper, the peak value of the impact force increased and the supply flow rate increased. It was also found that the peak of the impact force occurred continuously over time, rather than occurring only when the bottom of the waterway was reached. The results of this study will provide good information for examining the applicability of the impact force of the debris flow acting on the containment dam when the impact force calculation formula is used.