Abstract: It is discovered that corrosion perforation and breakage of the tubing stringhappened in the process of well repair at an injection-production well in Tahe oilfield. In order to find out the cause of corrosion failure, and take specific protective measures to ensure the safety of wellhole, the corrosion failure analysis of downhole pipe string was carried out by means of physical and chemical test, impact test, tensile test, and combined with scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), characterization analysis of corrosion products. The results show that the corrosion of tubing is electrochemical corrosion which was caused by H₂S-CO₂-Cl^--H₂O system. The CO₂ corrosion is dominant, and H₂S corrosion exists at the same time. Cl^- has a certain promoting effect on corrosion perforation. It suggests adding corrosion inhibitors or taking a surface coating, plating, and tubing lining to improve service life of oil pipe.