Abstract: There are reductions of a part of vanadium and titanium oxides on interface between slag and hot metal during V-Ti-bearing magnetite smelting in BF. These reactions result in difference of chemical composition and temperature between slag and roughing slag. The measurement and analysis results of temperature and composition of slag,roughing slag and hot metal show that reduction reactions on slag-hot metal interface make it possible that Ti （C, N ） content is about 0.2%~0.3% more and TiO+Ti₂O₃ content is about 0.3%~0. 4% more in roughing slag than that in slag,and the temperature of slag is about 25℃ higher than that of roughing slag,temperature of hot metal is about 5-6℃ higher than that of roughing slag. It is a particular phenomenon of V-Ti-bearing magnetite smelting in BF.