The corrosion behavior and corrosion mechanism of TC4 titanium alloy OCTG in severe CO₂ environment were studied with high temperature and high pressure and stress corrosion cracking (SCC) test, as well as electrochemical in-situ measurement techniques. The results show TC4 titanium alloy dominates the excellent resistance to uniform corrosion, local corrosion and SCC in high temperature and high pressure CO₂ corrosion environment, and the uniform corrosion rate is only 0.0012mm/a at the temperature up to 220℃. The anodic polarization curves of TC4 titanium alloy have the obvious passivation zone in CO₂ environment, and the corrosion reaction is controlled by anodic process. With temperature increased, the corrosion potential and polarization resistance of TC4 titanium alloy decrease, which indicate that the thermodynamic driving force increase, while the dynamic resistance decrease of the electrochemical corrosion, thus the corrosion rate of TC4 titanium alloy increase. However, the protective potential and pitting potential of TC4 titanium alloy are higher enough in high temperature CO₂ corrosion environment, and the polarization resistance is up to 2328.2Ω.cm₂ at 180℃, which still give TC4 titanium alloy the good passivation and re-passivation ability and the superior resistance to CO₂ corrosion at high temperature.