Abstract: GWAC (Ground-based Wide Angle Cameras) is the ground-based observation instruments of the sino-french cooperation SVOM astronomical satellite. Mini-GWAC is the pre-research project and supplement of GWAC.From the aspects of fault diagnosis methods, technical design plan and fault diagnosis platform, this paper describes the research and design process of fault diagnosis system in detail. Based on Mini-GWAC, we combine expert system theory and fault diagnosis analysis and use them to study the fault diagnosis expert system. Research results of this fault diagnosis system show that it can significantly improve the reliability of telescopes, reduce maintenance cost, improve the efficiency of observation and offer technical experience for application to other telescopes.