In view of inherent insufficiency of traditional fault diagnosis expert system in the aspect of knowledge representation, together with the characteristics of fault tree, hierarchical model and expert system, this paper puts forward a knowledge base maintenance approach based on Object-Frame knowledge representation, in which domain specific knowledge is expressed by combinations of the relevant objects' states. Object Frame knowledge representation and knowledge management are discussed. Algorithms are proposed for integrality verification of five inconsistencies among Object Frame knowledge: contradiction, redundancy, subsumption, circulation, and reclusion. The techniques such as management of dynamic data structure, interface and display of inference pathway are also described. VC++ and Access are adopted in developing the system. Experimental results demonstrate that this method has the characteristics of simple process, low computation complexity and strong adaptability.