Abstract: In order to solve exchange of qualitative and quantitative in the process of debris flow risk assessment, this paper establishes a model of debris flow risk assessment based on Cloud Model theory. First, we obtain the numerical characteristics of ten classified factors according to the classification standard method. Then we use the forward cloud generator to evaluate the measured data and calculate the certainty degrees of each gully belonging to the four grades. Second, combining the evaluation factor weights, we calculate the maximum comprehensive certainty degree of each gully. According to the four debris flow gully measured data in Miyun county of Beijing, this paper evaluates their risk assessment with Cloud Model. Compare the Cloud Model results with extension evaluation results, we find that the results are mostly the same. Therefore, we can make conclusion that the cloud model method is reasonable and accurate, which can evaluate the degrees of debris flow risk.