Abstract <p>The high-temperature flow stress behaviors of 300M and AerMet 100 ultra-high-strength steels, which have been widely used in aerospace industry, were investigated. Isothermal compression tests for 300M and AerMet 100 ultra-high-strength steels were performed at the temperature range of 900–1200°C and at the strain rate range of &#xa0;0.01–10 s^–1. Based on the experimental data, physical constitutive models based on the dynamic restoration mechanism were developed for the two ultra-high-strength steels, respectively. In order to evaluate the prediction accuracy of the proposed constitutive material models, the predicted flow stress was compared to the experimental data. As a result, the correlation coefficient and average absolute relative error are 0.9988, 2.36% for the 300M steel and 0.9983, 2.74% for the AerMet 100 steel, respectively. The developed constitutive material models have the highest prediction accuracy among the constitutive materials models of 300M and AerMet 100 steels reported in previous studies.</p>