Abstract: Described here in the paper are the activities for development of the Φ139.7 mm×9.17 mm 95 super 13Cr martensitic stainless steel casing. The optimal design of the steel composition is made by taking such actions as properly controlling the contents of Elements C, Cr, Ni and Mo., etc. to inhibit development of δ ferrite, adding Ti to prevent intergranular corrosion, and reducing N content to avoid formation of TiN inclusion. The longitudinal rolling shaping process of the CPE push bench mill and the 1 000℃ quenching + 600℃ tempering heat treatment process are studied, and the mechanical properties, the microstructure, the surface quality and dimensions of the said casing are tested and measured. It is concluded via the analysis that all the properties of the 95 super 13Cr martensitic stainless steel casing are satisfactory to the requirements as specified under Standard ISO 13680:2020.