The effect of deformation temperature and strain rate on the fracture and strain hardening of boron steel was investigated through the analysis of large amount of experimental data tested using a Gleeble (3800) materials simulator. These features were further modelled by using a set of unified viscoplastic damage constitutive equations. To study the deformation behavior, isothermal uniaxial tension tests of 1500 MPa boron steel at different strain rates of 0.01–5.0 s−1 and different deformation temperatures of 550–850 °C were performed on a Gleeble 3800 materials simulator. Considering the difference between the deformation of the necking cross section and the centre measuring cross section of specimen at necking stage, a correction method of measuring strain at the necking cross section was developed. In addition, by taking temperature rise during deformation into account, a correction method of measuring stress was proposed. The true stress-strain curves were obtained based on the two corrections methods. The influence of deformation temperature and strain rate on the fracture and hardening was analyzed. A set of unified constitutive equations was adopted and determined from experimental data. The correlation between the numerical-computed and experimental true stress-strain data is presented. The average relative error is within the range of allowable experimental conditions and the predicted and experimental values can almost be consistent.