With the development of artificial intelligence technology, expert system technology is becoming more and more important in fault diagnosis. By introducing the theory of expert system, the technology applying expert system to fault diagnosis filed is proven feasible. And the software design of test system based on Labwindows/CVI and expert system based on information Retrieval are introduced separately. The realization of fault diagnosis and real-time fault diagnosis expert system is presented. After using the software, it is effective that the expert system realizes the intelligent failure diagnoses, and it can enhance intelligent grade of the fault diagnosis.