The invention provides a supersonic nozzle preventing from slag entrapment, belonging to the field of steel making. The supersonic nozzle is composed of a main oxygen channel and an auxiliary oxygen channel positioned on the periphery of the main oxygen channel, wherein a center hole of a Laval tube forms the main oxygen channel, a plurality of narrow-long orifices are formed in the Laval tube, and the orifices are positioned in the periphery of the center hole and form the auxiliary oxygen channel. An auxiliary oxygen flow forms a surrounded accompanying flow outside a central supersonic jet flow, a low pressure area generated by the supersonic jet flow is weakened and canceled, and the suction enabling steel slag to be involved in the nozzle is eliminated; meanwhile, the expansion and attenuation of the central supersonic jet flow can be much smaller, the supersonic jet flow is longer, and the penetration depth and the stirring intensity of the oxygen jet flow for a molten pool are improved; the gun position is heightened so that liquid steel splash and slag bonding of a gun head are reduced, and the service life is prolonged. In the RH vacuum refining process, the main oxygen flow impacts liquid steel and reacts with carbon in the liquid steel to generate carbon monoxide, the carbon monoxide overflowing the liquid steel generates secondary combustion with the auxiliary oxygen flow of the surrounded accompanying flow to heat a vacuum tank, and the temperature drop of liquid steel is reduced.