Abstract: In order to solve the problem of key parameters in predicting "valley-type" debris flow at irregular profiles, based on Manning's formula, this paper establishes an approaching mathematical model of "equivalent area substitution method", which completed calculation for the deepest mud level, the flow rate and the threat range. The result is close to reality. This paper select 10 profiles randomly in the affected area by debris flow in western Henan, by this model: ①the deepest mud level was calculated , the flow velocity, and the area size of the cross-flood profiles under the probability of rainfall once in 10 years, and in 20 years, 50 years, in 100 years. ②Moreover, this paper has done some research for the law of evolution with different rain intensity, and quantitatively analyzed the flood discharge capacity of each profile.③Combined with the judgment standard of debris flow intensity, the selected areas were classified into extermely high-risk areas, high-risk areas, medium-risk areas, and low-risk areas. Furthermore, the model can not only provide basic parameters for predicting various indicators of debris flow, but also provide scientific basis for preventing and controlling disaster of debris flow. Finally, the results of this research have a certain significance in the refined prevention and control of debris flow.