PURPOSE: To stably operate a blast furnace by accurately assuming ratio of ore layer thickness to the sum of the ore layer thickness and coke layer thickness in center part of the blast furnace with model equation and making this assumed value the specific value or less.

CONSTITUTION: Based on blasting condition, charging wt. ratio of the ore and the coke and temp. and gas composition distribution in the radius direction just below deposited surface in furnace top, the layer thickness ratio of the ore and the coke in the radius direction is decided so that gas flowing velocity distribution obtd. from pressure gradient corresponds to gas flowing velocity distribution obtd. from carbon and oxygen balance. Then, the obtd. ratio of the ore layer thickness Lo at the furnace center to the total (Lo+Lc) of the ore and coke layer thickness is controlled to be ≤0.17. By this method, variation of [Si] in tapped molten iron from the blast furnace is reduced and the stabilization of furnace condition is obtd.