Abstract: The effect of different smelting stages on the occurrence of vanadium in the slag during the aluminum thermal reduction for FeV50 alloy preparation was analyzed,the thermodynamic reduction limit of vanadium in the slag was calculated by the study of V-O and VO-Al equilibrium theory.The actual stable structure of vanadium in the slag was obtained by different means of phase analysis.The results demonstrate that the steady state of vanadium in the slag is VO when the slag and alloy coexist,while the stability of VO and V₂O₃ is related to the partial pressure of oxygen after slag discharge.VO would be further oxidized under the condition of atmospheric pressure with the equilibrium oxygen partial pressure of 0.41 Pa.The total vanadium in the slag decreases with the increasing of aluminum in alloy,and the theoretical vanadium in the slag is 0.16% and 0.10% when the aluminum content is 8.0% and 20.0%,respectively.During the actual smelting process,the main materials of vanadium in corundum slag are composed of reduced FeV alloy as the primary phase and composite spinel structure of Mg（Al,V）₂O₄ and（Mn,Fe）V₂O₄ in the form of isomorphism.