Abstract: The knowledge composition and representation of the Dam Safety Monitoring and Controlling Expert System are expressed. The storage and management of rule and frame representation methods have been implemented in the relation data base. Due to the combination of database and knowledge base, the difficulty of knowledge base construction and management and the “bottle-neck” of knowledge acquisition is settled in a degree. Meanwhile, a knowledge editor has been designed, associating with the knowledge characteristics of the Dam Safety Monitoring and Controlling expert system.