In the iron smelting process, a large amount of blast furnace (BF) dust enriched with lead, zinc, chlorine, potassium and other elements will be produced. The existence of these elements has a negative impact on the recycling of iron in the BF dust. Therefore, the separation of these elements is the primary condition for realizing the efficient recycling of the BF dust. In this work, TG-DSC comprehensive thermal analysis was carried out for BF dust, and the water-soluble characteristics of lead, zinc, chlorine, potassium and their volatilization characteristics in the vacuum reduction process as well as the phase of iron in the reduction slag were studied. The results showed that the smoke had obvious endothermic peaks at 744 and 963℃, which indicated that there was a strong reaction at this temperature. According to the water-soluble characteristics of lead, zinc, chlorine and potassium in the smoke, it was qualitatively judged that the main forms of the four elements in the smoke were ZnCl2, KCl, ZnO, ZnFe2O4 and PbO. The vacuum reduction can effectively extract lead, zinc, potassium, chlorine and other elements from the blast furnace dust. Under the furnace pressure of 10 Pa and the temperature of 1100℃ for 30 min, the volatilization rates of lead, zinc, potassium and chlorine in the dust were 99.90%, 99.76%, 98.31%, and 99.70% respectively. The existing forms of chlorine in smoke were mainly ZnCl2 and KCl. Chlorine volatilized mainly in the form of ZnCl2 at 400~600℃ and KCl above 600℃. In addition to the volatilization of zinc in smoke by ZnCl2, zinc in smoke was volatilized by the reduction of ZnO and ZnO?Fe2O3 to metal zinc at high temperature stage. The volatilization of potassium was mainly KCl, and the volatilization of lead was caused by the reduction of PbO by carbon in smoke to metal lead vapor. The iron in the blast furnace dust was mainly Fe2O3. Fe2O3 was reduced to Fe3O4, FeO and Fe by vacuum reduction at 895℃ for 30 min, and Fe2O3 was basically transformed into Fe with good crystallinity at 1075℃ for 30 min.