To analyze the potential safety problems in the long-term operation of concrete dams, the degree of safety for concrete dams was quantified based on the long-term monitoring data. A safety evaluation index system was established by analyzing the essential safety factors affecting concrete dams. Then, the subjective weight based on analytic hierarchy process (AHP) and the objective weight based on data independence and data fluctuation (DIDF) theory were used to calculate the combination weight of each index. Finally, a comprehensive evaluation model for the long-term safety of concrete dams was constructed based on the ideal point method. The validated result of an engineering example shows that the weight of each index and the safety degree of the concrete dam calculated by the model are in accordance with the actual operation of the project.