UAV is a complex mechatronic system, in order to meet the needs of fault diagnosis, based on the theory of fuzzy mathematics, and integrate case-based reasoning into fuzzy inference machine. This paper focuses on how to determine the fuzzy relationship matrix and the principle of case-based reasoning, described in details of the case matching process, put over a new fuzzy inference mechanism, ultimately, design and implementation of system functions. It is shown from application results that this method improve the diagnostic process efficiency, accuracy and reliability.