Cumulation slope of debris flows are majorly controlled by lower-running landform slope and flow characteristics. It os neccessary to think over landform slope of samegrade stream-system, so that it can have comparison with each other. Predicting desposit model:Q^``_di=20.87C^4.42_vt+1.23C^3.31_vt×Q_u(20°≤Q_u≤30°). The exprimental data have reached the relatively notable level the 85% belivable range are 0.8893<ρ<0.9995. These researches will provide important parameter in controlled prevention of debris flow for predicting cumulation slope.