A Ternary Model is established for heat transfer in a reheating furnace. Temperature field for furnace walls was solved by implicit difference of non-uniform gridding. The temperature of billet surface was dealt with for coupling the finite difference method with the Ternary Model reasonably. Finally the 3# reheating furnace in Baosteel was simulated. Temperature fields of billet and walls are solved by the proposed approach, and the results are analyzed, which provides theoretical basis for thermal operations as well as the online applications of the Ternary Model.