Combining the successful applications in AI, in this paper, an expert system is studied and designed for evaluating the safety of hydraulic metal structures, whose goal is compute the reliability of hydraulic metal structures. Applying the techniques of AI, a framework is made up for evaluating the safety of hydraulic metal structures. The framework of knowledge base system is designed and presented with the domain knowledge. Based on the theory of relational database, the conceptual and logical views of database system are designed and analysed. Additionally, method base system is designed. A practical example is given to illustrate the process of using this system. This system has features of practical and advanced and expand.