Aiming at the high occurrence of accident at broken tailing dam and its significance in safety, the defects of evaluation methods currently used were pointed out. Considering that the safety system was a multiple-factor and multiple-layer system, a new evaluation based on fuzzy math was presented. A more rational comprehensive evaluation index system is proposed. The weight of each factor was also obtained, and corresponding safety evaluation model was set up by fuzzy math. The model is applied to lead-zinc tailings dam of QingshuiTang in Hengyang City of China. Results show that this method is practicable and reasonable. It provides a new method to evaluate stability of tailing dam.