Abstract: There are many interacting and coupling factors that affect the stability of tailings reservoir， so the dam-break risk assessment of tailings reservoir is uncertain. The hierarchical structure model is established according to the factors affecting the safety of tailings reservoir， analytic hierarchy process (AHP) judgment matrix is constructed， and the weights of each factors is obtained using AHP to combine qualitative analysis with quantitative analysis. The variable weight synthesis theory is introduced to AHP. Constructing the balance function and using the balance coefficient α to optimize the weight of each influence factor. The application of the engineering example results shows that this method can get more reasonable evaluation results. At the same time， the impact of single factor change on the evaluation results is analyzed， and the differences between the variable weight evaluation and the constant weight evaluation are comprehensively analyzed. The results show that the variable weight evaluation can better reflect the actual situation of the project， especially when the index parameters are poor， the variable weight evaluation can significantly reduce the score.

Key words: tailings reservoir, dam-break risk, risk assessment, AHP, variable weight analysis