Abstract: Risk of dam break not only depends on the probability of dam failure events,but also on consequences.When the dam break probability is known,the more serious the dam break consequence,the higher the dam break risk.The consequence is the direct impact of the dam break,including health effect(e.g.,death,injury),property loss,environmental impact,and social impact.Up to now,there are many researches in the field of life loss and economic loss induced by the dam break,but the researches on social and environmental impacts are relatively less.The index system is presented for the evaluation of the social and environmental effect of dam break,based on the analysis of the influence of the dam break on the society and environment.Multi-target methods and stage division are also proposed.The analytic hierarchy process is used to elicit the weight of each target.The fuzzy mathematics method is used to assess the degree of dam break impacts on the society and environment with the principle of maximum degree of membership.