The utility model discloses a top lance for RH vacuum refining. The top lance comprises a laval nozzle, a core tube, a top lance central tube, a top lance inner tube, a top lance outer tube and a top lance water-secluding pipe, wherein an annular constricted tube section and an annular divergent tube section are formed between the laval nozzle and the core tube. According to the top lance for RH vacuum refining, the annular constricted tube section and the annular divergent tube section are capable of accelerating a gas flow to the supersonic speed, and therefore, the working lance position can be increased, the splashing steel liquid sticking to the lance is reduced and the service life of the nozzle of the top lance is longer; an annular throat is arranged between the laval nozzle and the core tube, so that the oxygen blowing flow is increased and the heating efficiency of oxygen blowing decarburization and oxygen blowing aluminum addition are improved; oxygen, gas and desulfurization powder are conveyed to an RH vacuum chamber from respective different channels; the desulfurization powder is capable of reaching the surface of the steel liquid as being surrounded by a protective gas all around, and therefore, less powder is brought away along with vacuum pumping and the recovery of the desulfurization powder is high; compared with an existing top lance, the top lance disclosed by the utility model has the advantages that precision casting is not required and the manufacturing difficulty of the top lance for RH vacuum refining is obviously reduced.