Abstract: The traditional dam reliability and the safety coefficient calculation methods have two aspects of deficiencies:on one hand,it is impossible to give the accurate mean values of practical engineering design variables,and these values are greatly affected by many objective factors or artificial action.The effects have great degree of ambiguity.On the other hand,the traditional reliability theory employs Z=0 as the dam failure criterion to define the states of structural failure and security.But the damage of the dam from the safety limits is difficult to define.The transitional state of existence between reliablility and failure is a fuzzy area.Based on the above two issues,the fuzzy theory was applied to the stability of the tailing dams considering both the fuzziness of tailing dam failure and the main variables and parameters.The fuzziness and the randomness of the tailing dam project were integrated.The case studies show that the results and the actual situation are in good agreement,and that the method proposed,more scientific and rational than the traditional calculation methods,reflects the real situation for the stability of the tailing dams and provides a new way to analyze the stability of the tailing dams.