The present paper investigates the influence of O2 on X80 steel under the CO2 environment through polarization curves, EIS, and employing characterization by corrosion images and mechanisms, using the test data of the environmental content of CO2 and O2 in an oil field, while the pressure of O2 is 0.082bar~0.15bar. The results show that O2 mainly have influence on the polarization process of X80 steel cathode, and in the low O2 pressure of 0~0.12bar, corrosion potential and corrosion current density of X80 steel essentially remains the same, and with the increase of O2 pressure to 0.17bar~0.22bar, comprehensive corrosion rate and the electric double layer capacitance all increase, and also the polarization resistance, diffusion resistance, and charge transfer resistance is reduced. This behavior can be attributed due to the fact that O2 destroyed the surface of X80 steel by the corrosion film resulting in local corrosion caused by the presence of CO2.