Abstract: The effect of CO₂ pressure (0.03-0.26 MPa) on corrosion behavior of 20 steel in CO₂/aqueous two-phase stratified flow liquid phase medium was studied by weight loss method, scanning electron microscopy, and X-ray diffraction. The results show that the corrosion rate of 20 steel increased rapidly when the CO₂ pressure increased from 0.03 MPa to 0.11 MPa, and the corrosion rate increased slowly after the CO₂ pressure exceeded 0.11 MPa. The corrosion rates of 20 steel under different test conditions were greater than 1.193 mm·a^-1, indicating that 20 steel was severely corroded. 20 steel surface was covered with uniform and loose floc corrosion products, and a net floc structure was formed. The corrosion products mainly consisted of iron oxidation and FeCO₃. With the increase of CO₂ pressure, the compactness of the corrosion product film increased, the particle size of the corrosion products decreased, and the morphology of the corrosion product changed from flocculent, needle-like, and granular to scaly.