A method for operation of a flash smelting furnace comprising a reaction shaft, a settler connected at one end thereof to the lower portion of the reaction shaft and having a slag discharge port and a matte discharge port disposed on the side thereof, an uptake connected to the other end of the settler and at least one concentrate burner disposed to at least one of the top of the reaction shaft and the ceiling of the settler, in which the concentrate burner comprises at least a concentrate shoot, an oxygen blowing tube inserted in the concentrate shoot and an auxiliary fuel burner inserted into the oxygen blowing tube. In this method, the lower end of the oxygen blowing tube is protruded downward to lower than the lower end of the concentrate shoot and an amount of oxygen at least greater than that required for the auxiliary fuel is blown as an industrial oxygen by way of the oxygen blowing tube into the furnace. Oxygen efficiency can be improved remarkably while the rate of dust occurrence can be reduced.