The research results of dam aging and disease assesssment at home and abroad are comprehensively reviewed.On these bases, the dam disease index is put forward to judge the disease degree of dam, and the calculation method of the index is provided. According to the disease index, the dam disease degrees and dangerous conditions are respectively divided into five corresponding grades. The assessment model of possibility for dam breach based on dam disease index is developed, the dam breach index in the model is used to judge the possibility of dam breach and the possibility of dam breach is divided into five corresponding grades according to the index. The assessment model has been applied to evaluate the possibility of dam breach in Shaheji reservoir. And the evaluation result shows that the dam breach index is applicable for judging the possibility of dam breach. The model could be a reference for the possibility assessment of dam breach of dangerous reservoir. We suggest that the model should be gradually popularized, and the evolution law of dam disease as well as its correlation with the possibility of dam breach should be further studied.