Debris Flow in South Korea occurs frequently during the rainy season in summer. Especially localized rainfall due to abnormal weather conditions has caused many slope failures. Slope failures appear mainly in the mountainous Kangwon-do district. Debris Flow, which is one type of slope failure is an important cause of damage to river roads. Research on the occurrence and causes of debris flow is very limited. Accomplishment of model experiments with small and large gravels, we analyzed characteristics of debris flow under rainy conditions. The objective of this investigation is to evaluate the shock power of debris flow and to improve the design criteria for protecting structures against debris-flow.