Electro-hydraulic servo valve is an important part of aircraft brake system, which affects the safety of aircraft landing . In order to solve the problem of frequent failure of a certain type of electro-hydraulic servo valve, a model of electro-hydraulic servo valve of the brake system is established by using the regression analysis method. According to the analysis model and the fault symptom criterion, the recent working data of the electro-hydraulic servo valve are analyzed and the fault symptom is diagnosed. The results show that the method can accurately diagnose the fault symptoms of the electro-hydraulic servo valve.The early fault symptom diagnosis can detect the potential fault of the electro-hydraulic servo valve in advance, reduce the fault rate, improve the safety and reliability of the aircraft brake system significantly, and also help to optimize the maintenance strategy and reduce life cycle maintenance costs of the aircraft.