Abstract: Operation reliability of a water conservancy information system is related to the normal operation of water conservancy work.In order to comprehensively evaluate the operation reliability of water conservancy information systems, the main problems that may endanger the operation reliability of the systems are considered as an evaluation system, and the influencing factors of the systems' operation reliability are analyzed from four aspects: operating environment, hardware, network system software and human factors, finally a multi-level operation reliability evaluation index system containing the criterion level, target level, and state level is established.We use AHP method and the improved CRITIC method to determine the evaluation index weights, and build a comprehensive evaluation model of water conservancy information systems based on cloud model.Taking a decision support system in a water supply project as an example, the operation reliability of the system is studied and analyzed, and the comprehensive evaluation results are visualized and intuitive by using Python software programming.The results show that the operation reliability of the decision support system is closer to excellent and consistent with the actual situation, which verifies the feasibility of the evaluation model and provided a reference for research on the operation reliability of water conservancy information systems.