Abstract: In view of the movement trend fault of the drive system of the weapon cabin door of a certain type of aircraft, a fault tree is established to carry out the failure analysis. The result is that the seal ring of the servo valve sleeve is damaged due to the imperfect assembly process, which blocks the nozzle oil filter, and the servo valve is extremely biased, and the drive system of the weapon cabin door can only move towards the opening direction. Based on the theoretical analysis and AMEsim simulation model, the fault mechanism of the servo valve's positive direction deviation caused by the nozzle oil filter blockage is studied. The improvement measures such as improving the assembly process, increasing cleaning inspection, and enlarging the contaminant capacity are put forward to prevent the servo valve failure caused by the internal redundancy.