Through analysis of faults and failure symptoms of the condenser

a knowledge base of diagnositic expert system for condenser’s performance has been established by using rule representing method based on regular production mode. Because of the uncertainty of facts and rules

the subordinateness and credibility are used to process the fuzzy knowledge. Taking a rule in knowledge base of performance diagnosis as example

the subordinateness of symptom and the credibility of rule have been calculated

and a theoritical basis for establishment of the knowledge base being provided.