Abstract: Corrosion behavior of four kinds of S135 steel in polymer drilling fluids containing CO2 is investigated using high temperature high pressure autoclave. The results shows the average corrosion rate increases initially and then decreases as the rise of temperature or CO2 partial pressure; and increase as the flow velocity goes up. Average corrosion rate of S135 steel in dynamic liquid phase exceedes that in dynamic gas phase, and corrosion severity of S135 steel is listed as S135(A)＞S135(B)＞S135(C)＞S135(D). In this corrosion environment(temperature100℃, CO2 partial pressure 3MPa, velocity of flow 2m/s, exposed time 96h), local corrosion of gas phase of S135 steel is mild and pitting corrosion coefficient is 1.12~1.49, while that of liquid phase of S135 steel more serious and its coefficient 1.40~5.22. S135（D）drill pipe is recommended to use in polymer drilling fluids containing high CO2 concentration, and S135（A）or S135（B）abandoned.

Key words: S135 steel, CO2 corrosion, polymer drilling fluids, general corrosion, local corrosion, drill pipe