Abstract: The corrosion resistance of X65 steel subsea pipeline in CO2/H2S corrosion environments was studied by the high-pressure high-temperature autoclave and electrochemical test. The results showed that under the condition without corrosion inhibitor. the corrosion rate and localized corrosion risk of X65 steel under the 0.25 MPa total pressure condition were lower than under the 0.7 MPa total pressure condition obviously. The corrosion rate of X65 steel reduced observably when 100 mg/L corrosion inhibitor was added, showing excellent inhibition efficiency. The result of electrochemical test agreed with the simulated corrosion test. The corrosion risk of X65 steel was decreased by reducing the total pressure to 0.25 MPa, separatting a part of corrosion gas, so X65 steel can be used as subsea pipeline in oil and gas transportation in the corrosion environment with corrosion inhibitor addition.