Abstract: Based on the sub-molten salt process that vanadium and chromium in vanadium slag can be efficiently and selectivity converted into soluble salts at low temperatures,the main phase evolutions,occurrence and change laws of vanadium and chromium elements,and micro zone conversion rate of vanadium and chromium for vanadium-chromium slag before and after the sub molten salt reactions were studied.The results show that the vanadium-chromium spinel with lattice defects on the surface is more favorable for the lattice substitution of O^2- than the dense vanadium-chromium spinel,and the decomposition of vanadium-chromium spinel with the defects is accelerated.The recovery rate of Cr element before and after the sub-molten salt reactions is 99.63%,while the recovery rate of V element is 90.01%.The micro zone conversion rate of the main vanadium phases proves that the increase of vanadium content in Fe₂O₃ after the reactions of sub-molten salt is the main reason for the decrease of V recovery rate.