To solve the oil leakage problem of the hydraulic tank of an aircraft,based on the working principle and application environment of the hydraulic tank,the fault causes were analyzed from scratch,machining,assembling and design.Through metrological testing and theoretical analysis,it is confirmed that the cause of oil leakage in the hydraulic oil tank is that the width of the piston sealing groove is too large,and the material and size of the sealing ring are not selected properly,which leads to the insufficient rigidity of the sealing ring and the torsion fracture after rolling in the sealing groove for many times.In view of the oil leakage fault of the hydraulic oil tank,the sealing ring and groove were redesigned,the durability test of hydraulic oil tank was carried out.During the test,there is no oil leakage in the hydraulic oil tank,and it is found that the internal structure of the oil tank is complete and the sealing ring is not damaged after decomposing the hydraulic oil tank,which indicates that the oil leakage fault is eliminated after improvement.