Abstract: During the drilling of deep wells and ultra-deep wells, unsuitable tension-torsion coupling results to the failure of drill pipe. Therefore, it is necessary to study the combined tension-torsion resistant loading capacity of drill pipe. The combined tension-torsion loading test methods of pre-torsion followed by tension and pre-tension followed by torsion were used to analyze the interaction laws between the tensile stress/strain and torsional stress/strain of V150 drill pipe. It was found that during the pre-torsion followed by tension, both the preload shear stress and tensile yield strength were reduced; during the pre-tension followed by torsion, both the preload tensile stress and torsional yield strength were reduced. When material yielding occured, the tensile stress and shear stress were in accordance with the tension-torsion ellipse strength criterion, and the elastic deformation safety range of this tension-torsion ellipse strength criterion was 24.5% higher than that of von Mises strength criterion. The results showed that the combined tension-torsion resistant loading capacity of drill pipe designed according to the von Mises strength criterion was conservative to some extent, while the tension-torsion ellipse strength criterion included two benchmark parameters of tensile yield strength and torsional yield strength. Such criterion perfectly aligned with the experimental data and exhibited high engineering application value.