Abstract: A water delivery pipe in an oil field leaked. The leakage reason of the water pipe was investigated through the analysis of macroscopic appearance, chemical composition, microstructure, corrosion products and water sample. The results showed that the long-term synergistic effects of CO₂ and Cl^- dissolved in formation water caused localized corrosion and eventually leaded to corrosion perforation of the water pipe. The inner wall of the water pipe corroded first because of the CO₂ dissolved in formation water. And the temperature of transportation medium was close to the first corrosion maximum temperature of CO₂, which accelerated the CO₂ corrosion rate. At the same time, Cl^- penetrated through the loose FeCO₃ corrosion product film to generate autocatalytic acidification, which accelerated the dissolution reaction of anode.