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The electrochemical corrosion behavior of X70 pipeline steel under four different CO₂ pressures was investigated by electrochemical test methods and scanning electron microscope analysis, based on the simulated environment of the extracted water of natural gas transmission pipeline in an oilfield of Xinjiang. Results showed that in simulated extracted water solutions with high chloride ion content, the electrochemical impedance spectra(EIS) and polarization curves indicated that the corrosion of X70 steel specimens became increasingly severe with increasing CO₂ pressure(0.5, 1.0, 2.0, 3.0 MPa). The results of the loss-in-weight experiments showed that the corrosion rate of the X70 steel specimens increased with increasing CO₂ pressure, with a maximum corrosion rate of 2.573 9 mm/a at a pressure of 3 MPa. In addition. the XRD results indicated that the corrosion products were mainly FeCO₃. The SEM results showed that the pitting on the surface of the specimen became increasingly severe with increasing CO₂ pressure, and the surface of the specimen became increasingly rough. These results were attributed to the effect of high pressure CO₂ and pitting exacerbated by high Cl^- concentrations. Hence, it could be found that high CO₂ and Cl^- had a serious damaging effect on X70 pipeline steel. This work provided reference and guidance for the prevention of this type of corrosion.