Abstract: Described in the assay are the manufacturing process and key control techniques for the 20MnTiB quenched-tempered seamless steel tube for making of hi-strength,medium-heavy wall cylinder casing,and quality of the tube itself. Thanks to employment of the combined process of converter/electric steelmaking + LF refining + tuberolling + quenching & tempering treatment,the said seamless steel tube stays with high steel cleanness,and all the performance target values and dimensional accuracy up to the technical requirements as specified by the customer. The comprehensive properties of the said tube is better than that of the 27SiMn quenched and tempered seamless steel tube.