Abstract: According to the special requirements for the oil casing performance to meet the need by domestic shale gas production,the chemical composition design of the Cr-Mo-V series coil is optimized.Then the Φ139.7 mm×12.7 mm Q125 SEW oil casing is developed with the manufacturing process of hi-frequency ERW+hot-stretch reducing+full-length quenching-tempering treatment.The geometric dimensions,the mechanical properties and the collapse strength of the trial-manufactured casing are tested.The test results demonstrate that the casing has high dimensional accuracies,i.e.,ovality≤0.5%and uneven wall thickness≤5%,and good strength-toughness mating,and that the casing has yield strength≥862 MPa,tensile strength≥931 MPa,impact energy at 0℃≥60 J,and excellent anti-internal pressure and collapseresistant performances.Therefore the casing is up to the requirements for safe service in shale gas production.