This paper has established a mathematical model for the simulation of steel coil's heat transfer during the annealing thermal process in an HPH furnace. The equivalent radial thermal conductivity is adopted by a statistical analysis regression approach through the combination of a large quantity of production data collected in practice and theoretical analyses. The effect of the number of coils on circulating flow gas is considered for calculating the convection heat transfer coefficient. The temperature within the coil is predicted with the developed model during the annealing cycle, including the heating process and cooling process. Parametric studies have been performed to evaluate the impact of equivalent radial thermal conductivity, coil diameter, and coil width. The good consistency between the predicted results and the experimental data has demonstrated that the mathematical model established is scientifically feasible, and the effective method of calculation for a coil-equivalent radial heat transfer coefficient and circulating gas flow has been identified successfully, which largely enhances the operability and feasibility of the mathematic model. The results provide a useful insight and guidance in the operation and control of HPH furnaces.