Abstract: The corrosion mechanism of N80 steel tube was proposed through the analysis of morphology and composition of corrosion products on surface of hanging rings at multiple thermal-fluid injection site, and was verified by the composition analysis of the failed tube at site. The effect of temperature (120-280 ℃) of multiple thermal-fluid, CO₂ partial pressure (2-18 MPa) and O₂ partial pressure (0-1 MPa) on the corrosion behavior of the tube was studied by laboratory simulation corrosion tests. The results show that the corrosion reaction of the tube included CO₂ corrosion, O₂ corrosion and hydrogen corrosion. The carbon content of the failed tube at site was lower than the standard requirements, verifying the correctness of the corrosion mechanism. With increasing temperature, the corrosion rate of the tube increased first, then decreased and then increased. With increasing CO₂ partial pressure, the corrosion rate basically unchanged, then increased and then stabilized. With increasing O₂ partial pressure, the corrosion rate sharply increased first and then stabilized.