Abstract: Microstructure examination, hardness testing, chemical composition analysis, and macro and micro observation were carried out to analyze the failure mode of a J55 oil tube. The results show that the failure mode of the J55 oil tube was stress corrosion fracture. The failure cause of the tube was analyzed based on analyzing the manufacturing process, service environment and working mechanism. Local abnormal microstructure near fracture surface is the main reason for the fracture. The local abnormal microstructure might be caused by contacting cold liquid during the process of rolling or burning near the tube.