The work aims to study the corrosion electrochemical characteristics of N80 casing steel under different CO2 partial pressures at 80 ℃ and 140 ℃ for the typical temperatures in the recovery stage and sock stage in thermal recovery process. Potentiodynamic polarization curves and electrochemical impendence spectroscopy (EIS) were tested by high temperature and high pressure electrochemical autoclave with three-electrode system. The results of the electrochemical impedance spectroscopy were fitted and analyzed with ZSIMPWIN. Corrosion simulation test was conducted by high temperature and high pressure autoclaves, and the microstructure of corrosion scale was observed by scanning electron microscope (SEM). At 80 ℃ and 140 ℃, the corrosion of N80 steel under CO2 partial pressure 0.5~4.0 MPa was controlled by cathode. As CO2 partial pressure increased, the corrosion potential shifted positively and the corrosion current density increased. The EIS plots of N80 steel at 80 ℃ presented three time constants, capacitance loop in high frequency, inductance loops in mid-low frequency, and capacitance loops in low frequency. However, the inductance loops in mid-low frequency disappeared when the temperature reached 140 ℃ and only two time constants existed, capacitance loop in high frequency and capacitance loop in low frequency. Through the comparison of fitting results in EIS and the microstructure of corrosion product in immersed experimental sample, the corrosion scale resistance Rc and the charge transfer resistance Rt increases as the temperature rises, the porosity of corrosion scale decreases and the corrosion scale enhances the protection to the substrate.