Abstract: A method for operating a blast furnace, characterized by: adding a prescribed volume of blast furnace gas to an air for blast fed to a hot stove; oxidizing, in the hot stove, CO contained in the blast furnace gas into CO.sub.2 and H.sub.2 contained therein into H.sub.2 O to prepare a blast containing CO.sub.2 and H.sub.2 O and additionally heated by the above-mentioned oxidation; blowing the resultant blast containing CO.sub.2 and H.sub.2 O into a blast furnace through tuyeres thereof; thereby controlling the calorific value at the portions around the tuyere exits as a result of the endothermic effect produced by the reactions at the portions around the tuyere exits of the CO.sub.2 and H.sub.2 O contained in the blast with red-hot coke in the blast furnace wherein the amount of the blast is substantially equal to that of a blast without addition of a blast furnace gas.