This paper proposes a novel approach to estimate the temperature-dependent total emissivity based on the isothermal cooling process. The realizability of the ideal isothermal cooling phase has been verified through the finite-element model, even for specimens with low thermal conductivity. During the cooling process, the temperature difference of the specimen can be less than 0.8%. Moreover, based on the temperature curve of isothermal cooling, nonlinear total emissivity can be calculated using the inverse method over a broad temperature range, e.g., 500-1200 K, and the relative errors will be less than 8.83% with virtual test data. For a real-world application, we introduce the Savitzky-Golay (SG) filter to weaken the effect of noise on computation precision and successfully gain the smooth temperature-dependent total emissivity. (C) 2018 Published by Elsevier Ltd.