Abstract: The impact force of debris flow is the main cause of damage and destruction of check dam. In high altitude area, due to high mountains and deep valleys, serious physical weathering of surface materials, a wide range of source materials gradation, high frequency of debris flow occurence and high impact force, the damages induced by debris flow to the check dam are significant. To study the impact characteristics of the wide graded debris flow on check dam in high altitude area, the debris flow developed in Tibet is taking as a prototype. A physical test model of the impact check dam of wide graded debris flow is established. The unit weight of debris flow, the slope of flume and the maximum particle size of debris flow solid are selected as variable factors. 27 groups of flume tests were carried out to study the characteristics of impact force. The results show that: (1) Wide-graded debris flow mainly undergoes three contact evolution stages during the process of impact retaining dam, i.e. impact climbing-rolling return flow-accumulation and silting. The smaller of the debris flow volume weight could lead to a higher climbing distance, and more obvious stage performance of sourcing and sliting process. (2) The impact force in front of the dam decreases with the increase of the bulk weight of wide-graded debris flow. Under the same slope and gradation, a larger the bulk weight of debris flow materials lead to a lower velocity of the debris flow materials and less impact force, because it is more difficult to carry solid material sources. (3) The impact force in front of the dam increases with the increase of the groove gradient. The larger the groove gradient, the greater the flow velocity and flow depth of wide-graded debris flow, the greater the impact force of debris flow. The larger the particle size of solid phase of debris flow, the more significant the impact of slope on impact force. (4) The impact force in front of the sand bar increases with the increase of the maximum particle size of the solid phase of the wide graded debris flow, and the change trend is more significant than when the volume density of the debris flow and the slope conditions of the groove change. The maximum particle size has no obvious regular relationship with the velocity and depth of the debris flow. The research results will provide certain data reference for the prevention and research of wide graded debris flows.