Abstract: The speed of the decay of the jet stream discharged from the five-orifice lance nozzle has been measared. The result shows that the speed of the decay of the central and the peripheral jet's velocity isn't identical which is caused by the difference of the jet's surrounding condition. When the diameter of the central orifice(C.O)is equal to the diamefer of the peripheral orifice(P.O), the velocity of the central jet is twice as fast as the velocity of the peripheral jet, in the condition of the common lance height. In order to make fuller use of these jets to agitate effectively and homogeneously the molten bath, the velocity of the central jet should be equal to, or slightly greater than, that of the peripheral one at the surface of the molfen bath. In order that this object can be obtained, the design of the five-orifice nozzle ought to make the area of C. O(Ac) less than that of each P. 0(Ap). According to the measured result, Ac/Ap should be equal to 0.6~0.8.