System component failure diagnosis is provided. In response to determining that a number of component failure cases corresponding to a complex system stored in a historical diagnosis database is less than a pre-defined threshold number of component failure cases, a system component failure root cause is predicted using a rule-based reasoning method. In response to determining that the number of component failure cases corresponding to the complex system is greater than or equal to the pre-defined threshold number of component failure cases, the system component failure root cause is predicted using the rule-based reasoning method and a machine learning method. The diagnosis accuracy of the system component failure root cause predicted by the rule-based reasoning method and the machine learning method is calculated using a cross-validation method. The performance of the rule-based reasoning method and the machine learning method is evaluated using a statistical process control method.