At present, aircraft fault diagnosis methods have been used in many engineering applications. Among them, most methods considered only a single case-based or rule-based diagnostic method, therefore the efficiency of those fault diagnosis methods need to be improved. In this paper, it proposed and studied a fault diagnosis method based on the integration of case and rule reasoning, and introduced the method into the fault diagnosis system of commercial aircraft ground operations support system. In this aircraft fault diagnosis method, rule-based reasoning is a leading part, and the case-based reasoning is a rear complementary part. This combination can maximize the use of aircraft Fault Isolation Manual (FIM) and case knowledge extracted from the maintenance records. Thereby it can increase first-time fix rate and reduce the invalid troubleshooting time. Taking the typical failure in an aircraft system as an example, the reasoning mechanism in fault diagnosis was illustrated. The historical flight data tests verified the effectiveness of the proposed fusion diagnosis method based on case and rule. The design of fault diagnosis based on the proposed method can provide a reference of building a more perfect expert system for aircrafts.