Abstract: The influence of yield ratio on the strain-hardening exponent, the true fracture strength, the uniform plastic deformation capacity and static toughness was discussed by analyzing the true stress-strain curve of two materials with different yield strength (steel grades of 105, 135, 150, 165) by heat treatment. The results showed that the yield ratio had no significant correlation with above parameters. It cannot be strictly required in the high strength drill pipe, good ductility is a key technology index to ensure the safety of high strength drill pipe. For the drill pipe of steel grade 150 which manufactured by special material and strictly heat treatment, although it’s engineering yield ratio is quite high, it still has a good comprehensive performance because of its high plasticity.