The invention relates to a model for optimally controlling a heating system of a large walking beam type heating furnace plate blank, which belongs to the technical field of industrial heating. A billet steel heating system optimizing model is adopted to optimize the order of entering the furnace for the billet steel of different steel type; the billet steel heating time and the temperature of each segment of the heating furnace are optimized; and the temperature change of the billet steel in the heating process is predicted. The model consists of a temperature control module of a single steel type of billet steel, and a heating optimal control module of multiple steel types of billet steel, wherein one module aims at simulating the heating process of a signal block of billet steel, and the other module aims at simulating the heating process under the condition of 10 blocks of billet steel entering the furnace, i.e. mixed loading furnace entering condition. The model is adopted to optimize the heating system of the billet steel so as to avoid the overhigh heating temperature of the billet steel and reduce the oxidation burning loss of the billet steel; reasonable heating time can be adopted to reduce unnecessary fuel waste and fuel consumption; and the model is conducive to scientifically and reasonably regulate the operation parameters of the heating furnace and meet the requirements on billet steel heating quality.