By injecting argon-chlorine, nitrogen-chlorine, argon-sulfur hexafluoride, argon-sulfur dioxide and other mixed gases into the melt of the furnace, the impurities in the solid metal can be greatly reduced, and the purity of the metal can be improved so as to obtain the highest purity of the molten metal as ingot material. It is the latest application of high purity metal smelting industry in recent years.