High speed air injection should be carefully determined to obtain better mixing in the melting furnace. In the study, the penetration length has been measured with the high speed air jet supply. Characteristics of the penetration length in the Melting Furnace were determined and discussed with the effect of air jet velocity and nozzle diameter. Air injection flow rate was varied from 0.05 to 0.5MPa at an interval of 0.05 and nozzle diameter was adjusted to be 5, 7, 9 and 12mm. The experimental results measured by CCD camera have four different flow incidents. The penetration length decreased with the increasing nozzle diameter because momentum grew less and less.