Abstract: Taking Hefeng Waidongshan debris landslide in Huangshan Anhui Province as a case, the ralationship between the deformation-develop process and the critical water content of debris landslide was studied by the discrete element method. And the critical water content was proposed according to the results, providing evidence for the study of warning criterion of debris landslides. The simulation results indicate that, rainfall leads to the increase of water content of the debris landslide, which will reduce its physical and mechanical properties, induced landslide. When the water content of Waidongshan landslide is less than 26%, the landslide is stable. When the water content of Waidongshan landslide is greater than 29%, the landslide will make deformation. The results showen that the critical water content of Hefeng Waidongshan debris landslide is between 26%～29%. the study of warning criterion of debris landslides, can be studied the relationship between the rainfall and the warter content of debris landslide further. So the critical rainfall can be proposed, providing the basis for the study of warning criterion of debris landslides.