According to the construction requirements of myriametric extra-deep well， the BG155V casing with good toughness， high-temperature strength， collapse resistance and delayed fracture resistance is developed on the basis of alloying technology and manufacture process optimization. The test results of batch production showed that the yield strength reaches over 1100 MPa， and the transverse Charpy impact energy at 0 ℃ reached 10% of the nominal yield strength， and the strength and low temperature toughness and microstructure of casing under different service temperatures were analyzed. It was found that the grain size level of the casing with controlled cooling process after hot rolling reaches up to 11. The fine grains ensure good toughness and delayed fracture resistance of the material， which improves the reliability of the casing in the myriametric extra-deep wells for the development of oil and gas resource.