Abstract: In CO₂-O₂ Environment under simulated temperature cycling conditions (100℃×72 h→60℃×72 h→100℃×72 h→60℃×72 h, 100℃×72 h→60℃×72 h→100℃×144 h, 100℃×72 h→60℃×216 h, called as 1^#, 2^#, 3^# schemes, respectively) in multi-thermal fluid injection oil recovery, immersion corrosion tests were conducted on 3Cr steel. The corrosion rate, corrosion morphology and phase composition of corrosion products of the test steel were studied. The results show that under the 1^# and 2^# schemes, the corrosion rates of the test steel were similar. The corrosion rate under the 3^# scheme was the smallest, and was 15.0% and 14.74% lower than those of the former two schemes, respectively. Under the three schemes, pits were observed on the surface of the test steel. The corrosion product scales were divided into two layers. The inner scale was dense, but had many tiny cracks; the outer scale was loose, and had many holes. The corrosion scales were mainly composed of Fe₂O₃, FeCO₃, FeOOH and Cr(OH)₃.