The invention provides a powder spraying desulfuration mechanism for performing RH (Ruhrstahl and Heraeus) on molten steel. The powder spraying desulfuration mechanism is composed of a desulfurizing agent delivery system and a spraying system, wherein the desulfurizing agent delivery system comprises a desulfurizing agent storage bin, a first rotary feeder, a physical strength sending tank, a receiving bin, a blowing assisting device, a spraying tank, a weighing device, an impulse type fluidifying device, a nitrogen module and an argon module, and the spraying system comprises a spray gun lifting mechanism, a spray gun and a vacuum groove. By virtue of calculating the resistance in the delivery process, the desulfuration device is specifically and additionally provided with the blowing assisting device, the stable transportation of a desulfurizing agent is guaranteed, a pipeline is easy to plug; and meanwhile, the position of the powder spraying of the spray gun is adjusted, the position of the spray gun is adjusted according to the pressure in the vacuum groove, the powder spraying penetrating power is enhanced, and the deep desulfuration purpose is achieved.