In order to objectively evaluate the safety state of diversion tunnel disease in Northwest China, the safety evaluation index system of diversion tunnel disease is established in view of the disease problems existing in the operation period of diversion tunnel in Northwest China. The weight of each index is determined by using Super Decision software and ANP method. Based on the traditional TOPSIS method, the grey relational theory is added to construct the safety evaluation model of diversion tunnel in Northwest China. The model is used to evaluate the safety of six typical tunnel sections in Pandaoling tunnel in Introducing Datonghe into Qinwangchuan Project, and the safety grade of each tunnel segment is obtained. The evaluation results are objective and accurate, which verify the scientific rationality of the established index system and model, and can be applied to the safety research of long distance water diversion projects.