A multi-function top lance with public channel is used to blow oxygen, inject powder and bake on vacuum cyclic treatment furnace of RH molten steel. Blowing oxygen and injecting powder are done with one nozzle in one channel. The channel is cleaned by air purging device when switching function from blowing oxygen to injecting powder or the inverse. Compare with the present top lance, the utility model can increase the space usage rate and cooling effect inside the top lance, reduce the cost of manufacture and operation, and optimize the function during vacuum cyclic treatment of RH molten steel.