Abstract: The potential chemical reactions of chlorine element in blast furnace were investigated by using the thermodynamic software(HSC Chemistry 6.0). The major chemical reactions at different range of temperature were analyzed,and the reaction behaviors were obtained under the three kinds of smelting conditions,ie,without the presence of alkali,with small amount and large amount of alkali,respectively.The results show that without presence of alkali the chlorine brought in by raw materials and fuels mostly generates HCl gas. When the alkali amount is small,chlorine is present in the form of HCl gas and alkali-chlorine. while chlorine mainly exists in the form of alkali-chloride if a large amount of alkali is present in blast furnace.. The obtained chlorine products rise along with the blast furnace gas. Some of chlorine product is absorbed in iron burden and coke and then fall down,some is discharged with blast furnace gas. In addition,small amount of chlorine element is absorbed by blast furnace slag. It is imperative that the chlorine products of blast furnace affect the smelting process of blast furnace.