Abstract: Case-based reasoning is applied to a faulty diagnose system. The method of building the faulty cased base and result base is discussed, and these bases are restored according to database. A method for the definition and calculation of teh relational degree based on the grey-relational theory and fuzzy-set theory is put forword so that similar cases can be found out accurately. A fundation is laid for future research.

Key words: case-based reasoning, fuzzy-set theory, grey-relational degree, faulty diagnoses