For the automatic control of hot metal temperature, a new simplified mathematical model of blast furnace has been developed on the following assumptions:(1) The working volume in the furnace is divided into five horizontal zones. Only the specified materials and reactions are considered in each zone.(2) By taking material balance, the flow rates of solid and gas at each zone are determined so that the amount of the material existed in each zone remains constant.(3) Heat balance is applied to solid and gas in each zone, respectively, taking account of their average temperature.(4) The reaction rates are formulated as the functions of operational variables on the basis of their step response characteristics.The temperature of solid and gas at each zone can be predicted by the adjustment of parameters in the model using actual operational data. Since the predicted solid temperature at the fifth zone (tuyere level) agrees well with the actual hot metal temperature, the validity of the model has been proved.At Kokura No. 2 BF, Sumitomo Metal Industries, Ltd., the model is being used for the automatic control and contributes to the stable blast furnace operation.