The thermal-mechanical properties of WHT1300HF high strength steel were tested by isothermal uniaxial tensile methodatvarious strain rates(0.05,0.2,0.5 and 1s-1)and temperatures(700.750,800 and 850℃)and analyzed by constitutive equations.The results show that increasing deformation temperature leads to significant reduction in the level of flow stress and work hardening exponent of the steel; however,increasing strain rate results in noticeable increase in the stress level and work hardening.Arrhenius-type constitutive equations were used to describe the flow behavior of the steel at elevated temperatures.With the constants of n,α,ln A and Q determined by the approximation method,the relative error between the calculated and tested flow stresses is smaller than 5.15%,suggesting a high level of confidence in the developed constitutive equations.