Control of the blast furnace hearth lining is an important aspect in ensuring efficient and safe operation of blast furnace production [1, 2]. The furnace lining plays a key role in protecting the blast furnace from high temperatures and chemically aggressive slag melt. Early detection of areas of increased wear allows you to plan preventive maintenance, minimizing downtime and loss of productivity. The article describes the developed three-dimensional unsteady furnace hearth model based on thermocouple data. The model makes it possible to estimate the shape of the furnace hearth and the temperature distribution in the furnace brickwork in three-dimensional and two-dimensional (graphical) form. To assess the condition of the furnace lining, the readings of thermocouples installed in the furnace lining of the blast furnace in the area of the three lower belts of refrigerators were used. The specified mathematical model can be used to control the blast furnace process at any time after capital repair of the first category.