Abstract: Adopting the definition suggested by the United Nations, debris flow risk is used to measure the expected losses (losses of lives, person injured, property damage, and economic activity disrupted) due debris flows for a specified area and during a reference period. Under the mathematical proposition of Risk is the product of hazard and vulnerability given by the United Nations, the present paper has obtained an approximate quantitative solution for empirically assessing debris flow risk. Site-specific debris flow risk assessment model is a multiple factor composite assessment model including seven factors, and site-specific debris flow vulnerability assessment model is a nonlinear complex function model including seven indexes, so site-specific debris flow risk assessment model is practically a synthetic model comprising of 14 variables. This paper has also discussed the classes of debris flow risk and their probability distribution. Among the five classes, from the statistical viewpoint, the very low risk class occurs with a probability of 16.88%; the low risk class occurs with a probability of 28.44%; the moderate risk class occurs with a probability of 27.46%; the high risk class occurs with a probability of 19.78%; the very high risk class occurs with a probability of 7.44%. A case study in Heishan gully of Yinmin copper mine of Dongchuan in Yunnan province has been used to demonstrate the procedures of the method for site-specific debris flow risk assessment.