As the diameter of the casing in the reservoir becomes larger and larger， and the well go deeper and deeper， the demand for strength and toughness of large-diameter perforating barrel becomes stronger. In order to ensure the safety of the perforating operation and improve the ability of the perforating barrel to resist external extrusion， it is necessary to improve the strength of the barrel and match higher impact toughness. Tianjin Pipe Corporation has developed big size Φ244.48 mm×11.99 mm high strength TP170P grade gun pipe. After heat treatment， the yield strength is over 1 200 MPa， and CVN 0 ℃ impact energy reaches to 110 J for longitudinal and 85 J for transversal. The gun pipe has good high temperature tensile performance and excellent low temperature impact toughness. At the high temperature condition of 300 ℃， the yield strength still reaches 1 056 MPa， and the low temperature impact toughness and brittle transition temperature is less than -40 ℃，this character assures the gun pipe can be used safely in the high temperature and ultra-deep well ， it has cold toughness in cold areas ， expanding the use range of the products. In addition， the steel grade has good resistance to hydrogen sulfide stress corrosion， hydrogen cracking ability and rolling thermal deformation ability.