Abstract: The oil leakage accidents occurred three times in one aviation engine in use. Based on crack macroscopic observation, metallographic examination, chemical composition analysis, stress measurement and fracture surface electron microscope observation for one of the oil tubes, the crack mechanism and cause were determined. The results showed that the cracks in oil tube were fatigue crack under large initial stress, the fatigue crack originated on the R outer surface of pipeline transfer mouth because of large assembly stress. The crack initiation also had certain effect and promoting by the impact of high pressure fuel and the vibration of tubing role and local unbonding of solder in the position of pipeline transfer mouth.