Abstract: Described here in the article are the development of the Φ273.05 mm×13.84 mm 140HC hi-strength/hicollapse resistant casing.Based on the chemical composition of the Cr-Mo-V medium carbon steel,the chemical composition of the steel is properly designed.And high dimensional accuracy of the product is guaranteed by means of adopting the continuous casting process of "converter melting+out-of-furnace refining+vacuum degas+electromagnetic stirring" and the prevision rotary rolling process.Also guaranteed is the proper mate between the strength and the toughness of the product due to use of the heat treatment process of "normalization+quenching+hi-temperature tempering".Relevant testing and inspection results show that the 140HC casing as developed stays with such characteristics i.e.,OD roundness ≤ 0.4%;WT evenness ≤ 10%;transversal impact energy-longitudinal impact energy ratio:95% approximately;and collapse strength:over 72.1 MPa.Moreover the dimensional accuracy and all the performance indexes are up to the design requirements,being worth using in the deep wells in the western oilfields of the country.