In view of the fact that flush flood and debris flow disasters occur frequently in the upper stream of Miyun reservoir,the theory of Bayes discriminatory analysis is firstly applied in predicting the natural disasters.System science and debris flow prediction theory are adopted to analyze internal elements and external environmental conditions of the system which influences the occurrence of flush flood and debris flow in the area.Accumulated precipitation of the preceding 15 days and intraday precipitation are introduced as model indexes and a set of prediction models is then established.By checking the model with oneself validation and cross validation,the accuracy for judging is 82.4%,which meets the requirement of Bayes discriminatory analysis that the accuracy of judged model should be more than 80%.Two validation results are consistent with each other and the model is stable.Therefore,the established model is credible and can be put into practical use.The research offers a simple and quick way for predicting flush flood and debris flow in the area and provide a support for the prevention and control of flush flood and debris flow in Miyun County,so as to reduce the loss caused by the two types of disaster.