In the paper, the exact definition of thermal value was proposed and the mathematical model of effective utilization degree of energy in batch-type heating furnace was developed to give the thermal value equations derived from Stalk's formula. It was achieved that the heat attached on the steel slab injected into the batch-type furnace uniformly would have higher thermal value when the intake time was closer to the end of heating; as for heat attached on furnace gas, the closer to gas supplying, the higher thermal value will be got. And higher thermal value of heat attached on steel slab could be achieved at higher productivity. The factors of steel slab such as overall dimension, physical properties, and heating initial condition and boundary condition, which affected the productivity of furnace, were pointed out to be influencing factors of thermal value.