Abstract: The morphologies,phase contents,existing forms and trace of vanadium in the roasted vanadium slag before and after leaching were comparatively analyzed. The results show that the morphology of the spinel transforms from compact and smooth surface to porous structure with unsmooth surface by roasting. There is no different in the phase species of the roasted vanadium slag and leaching residue by the MLA phase analysis data. However,the phase contents vary considerably between the roasted vanadium slag and leaching residue due to a great decrease of calcium vanadate. According to the test results of vanadium distribution,the solid solution of iron oxides cannot be leached by acid because of the impurities and plenty of vanadium dissolved in it. When the roasting time reaches to 360 min,the formed transition phase of pyroxene-calcium silicate hinders the diffusion of oxygen,leading to the package of vanadium in the solid solution which cannot be leached by acid.