Two methods for estimating the critical temperature(T_b) of thermal explosion for energetic materials (EMs) are derived from the Semenov's thermal explosion theory and two non-isothermal kinetic equations, dα/dt=A(1-α)e^-Ea/RT and dα/dt=A(1-α)［1+E_a/(RT)(1-T₀/T)］e^-Ea/RT, using reasonable hypotheses. We can easily obtain the values of the autocatalytic reaction activation energies (E_a), the onset temperature (T_e) and the initial temperature (T₀) at which DSC curve deviates from the baseline of the non-isothermal DSC curve of EMs, and then calculate the critical temperature (T_b) of thermal explosion by the two derived formulae. The results obtained with the two methods for nitrocellulose (NC) are in agreement to each other.