Abstract: For simulation the corrosive working conditions of a certain domestic oil field，the corrosion test is conducted with the high temperature/high pressure caldron and the weight loss method to investigate the effects of relevant environmental factors on the uniform corrosion rate of the BT80S-5Cr oil casing，including the test cycle，the temperature and the CO₂ and H₂S partial pressures. The results show that along with the extension of the test period，the uniform corrosion rate of the test steel gradually decreases，and the decrease tends to be steady and slow；and the test period of 360 h is the best test period for the BT80S-5Cr steel to measure the corrosion resistance under the simulated working conditions of the said oil/gas field；with the increase of test temperature，the uniform corrosion rate of the test steel gradually increases；the uniform corrosion rate of the test steel as tested at 100 ℃ is 1.67 times that of the test steel as tested at 40 ℃；With the increase of the CO₂ partial pressure，the uniform corrosion rate of the test steel gradually increases，and the uniform corrosion rate of the test steel with a partial pressure of CO₂ of 1.0 MPa is 10 times that of the test steel free of CO₂；along with the increase of the H₂S partial pressure，the uniform corrosion rate of the test steel gradually decreases，and the introduction of trace H₂S gas has a certain inhibitory effect on the electrochemical corrosion behavior of the test steel.