To overcome the drawbacks of the high price and low efficiency of the desulfurizer which is used in spraying magnesium desulfurization, an in-situ desulfurization method that using the high temperature in hot metal to generate magnesium vapor was proposed. In this paper, the generation of magnesium vapor using new desulfurizer was investigated, and the conclusions are: with the temperature increasing, diffusion velocity of magnesium vapor and reaction rate were accelerated; with the increasing of flow rate of carrier gas, the reaction rate were accelerated; the apparent activation energy of the generation of magnesium vapor using new Magnesia-based desulfurizer was 69.57 kJ/mol, and the process was controlled by diffusion.