Aiming at various problems in fault diagnosis of aircraft hydraulic pipeline system in complex environment, a leakage fault diagnosis method for hydraulic pipeline system was proposed based on probabilistic neural network . The main fault in aircraft hydraulic pipeline system was the pipeline rupture and leakage caused by the vibration of the pipeline system. The aircraft hydraulic pipe was modeled, and the natural frequencies of different hydraulic leakage faults under different working conditions were analyzed. By choosing the first five natural frequencies as the eigenvalues of fault diagnosis, the PNN probabilistic neural network diagnosis model was constructed.The experimental results of fault diagnosis using test samples show that the proposed method is effective. The method has high fault identification rate for hydraulic pipeline. The research provide reference for fault diagnosis of hydraulic piping system.