Abstract: The hot-deformation behaviors of low activation martensitic steel were investigated in temperature range of 850-950 ℃ and strain rate range of 0.001-1 s^-1 by Gleeble-3500 thermal simulation machine. The constitutive equation was established and its predictive ability of flow behaviors was evaluated. Hot processing maps of low activation martensitic steel at different strains were established. The results show that the material exhibits the characteristics of dynamic recrystallization at higher deformation temperature and lower strain rate. The prediction results of constitutive equation are in good agreement with the experimental results. The optimal parameter combinations for hot processing at true strain of 0.4 and 0.6 are determined as the interval of temperature of 870-930 ℃ and strain rate of 0.001-0.01 s^-1, and the interval of temperature of 920-950 ℃ and strain rate of 0.3-0.1 s^-1, respectively.