Because the relationship of faults and their expressions in FCCU system is a fuzzy one.The fault diagnosis model was based on the the relationship between FCCU fractionating system malfunction characteristics and malfunction symptoms. This model takes into account the influence of the acquirable symptoms and introduced symptom confidence and rule confidence. The expert knowledge of identifying the fault of FCCU was reviewed. In order to reduce the developing period of fault diagnosis expert system and increase its developing flexibility this paper had discussed a method by using of developing Visual C++ and expert system tool CLIPS the fault diagnosis expert system of FCCU fractionating system. This method has good transplant ability and can develop effective expert system frame in a short time．

CLIPS,    , VC++,    ,  FCC,    ,  Fault Diagnosis