Abstract: Based on the DEM, geomorphic features, land use types, soil types and soil moisture of the Hongshaogou watershed in Maerkan, the data of the annual precipitation and the precipitation data of 2015 were calculated according to the SCS model of runoff-confluence and debris flow June 30 Hongshao river storm-debris flow disaster scale. The simulation results show that the simulation accuracy of SCS model is more than 95% compared with that of debris flow field data, which shows that the SCS model runoff simulation and debris flow matching method can be applied to debris flow disaster assessment in the Small river watershed without rainfall observation data method.Using this method, the total debris flow triggered by the extreme heavy rainfall in Hongtaoogou is 5 times of the total debris flow occurred on 30 June, 2015.