Desulphurization slag is fugitive and difficult to be removed, and resulfurization is easy to happen in the magnesium-spraying desulphurization pretreatment of vanadium bearing hot metal in cheng steel.. According to special hot metal, the desulphurization rate can improve by 12.38% with optimization of major blowing flow and feeding speed, and probability of lance plugging gets small. After appropriate calcium-based desulphurization agent added before tapping, passivated magnesium utilizing rate increased by 8.66%. The result of slag skimming enhanced and the average resulphurization rate reduced by 0.006%, also the quality of vanadium slag did not be influenced.