Abstract: In a certain region,the super precipitation of overall uniformity will not lead to debris flow in valleys under similar conditions of landform.Debris flow occurs mainly due to the differences of the characteristics of bedrock lithology.When the bedrock structure is overall uniform,loss of the department of loose form is continuous and progressive;if the bedrock is made of hard rock interbedded with soft rock,or is damaged by linear geological structures,the bedrocks may be weathered differently,and the department of the loose form is in a pulsatile erosion state,which preferably provide materials for debris flow.