Abstract: The polarization curves of T225NG Titanium Alloy in high temperature and high pressure aqueous solution with different concentrations of chlorine ion and dissolved oxygen have been measured by electrochemical method, and its electrochemical behavior and corrosion mechanism have been analyzed. The active regions of the anodic polarization curves of T225NG Titanium Alloy have not been found in the test condition. Passive current density and corrosion of T225NG Titanium Alloy increases when the concentration Cl^- and dissolved O₂ becomes high. There is a formation of oxide film i.e. A region in the solution which Cl^- is below 0.005mg/L while there are formation of oxide film and release of Cl₂, i.e. A and B regions in the solution which Cl^- is above 0.02mg/L for the polarization curves of T225NG Titanium Alloy.