The flow stress behavior of grade G-105 steel(API standard) for oil drill pipe in hot compressive deformation was studied by isothermal compression tests on Gleeble-1500 thermal-mechanical machine.Referring to established empirical formulas,the constitutive equation of the flow stress for G-105 steel was obtained.For the grade G-105 oil drill pipe(φ114.3×10.92 mm),through proper design of the die and applying suitable process parameters,and using coupled rigid viscoplastic thermo-mechanical finite element method,the forming process of making upset on oil drill pipe was numerically simulated.The simulation results show that the internal transition section of the oil drill pipe is not only continuous and smooth but also long(up to about 220-250 mm). The flow stress behavior of grade G-105 steel (API standard) for oil drill pipe in hot compressive deformation was studied by isothermal compression tests on Gleeble-1500 thermal-mechanical machine. Referring to established empirical formulas, the constitutive equation of the flow stress for G-105 steel was obtained. For the grade G-105 oil drill pipe (φ 114.3 × 10.92 mm), through proper design of the die and applying suitable process parameters, and using coupled rigid viscoplastic thermo-mechanical finite element method, the forming process of making upset on oil drill pipe was numerically simulated. The simulation results show that the internal transition section of the oil drill pipe is not only continuous and smooth but also long (up to about 220-250 mm).