Abstract: Elaborated is the trial production process of the Q125 high-strength oil casing as per API Spec 5CT-2011, PSL-2.On the basis of the medium carbon Mn-Cr-Mo steel, the chemical composition is reasonably designed to make sure that the total alloy element content is ≤ 2.5%.For steel making, the process flow as used is EF→refining→vacuum degassing→CCround casting.During the processes of rotary-piercing and PQFrolling, it must be guaranteed that the work-piece undergoes hi-temperature big deformation in the austenite zone.And after rolling, theΦ127 mm×9.19 mm high-strength oil casing has to be quenched at(920±10)℃ and with a soaking time of 17 min., and tempered at(620±10)℃ and with a soaking time of 35 min.The testing and inspection results show that the said oil casing has been fully up to the requirements for yield strength, tensile strength, elongation, and impact energy(including statistic impact energy)as specified under API Spec 5CT-2011 for Q125 steel grade of PSL-2.