Abstract: The effect of additive agents on active lime desulfurization of boron-containing molten iron with high Si/S content was studied with injection method. The results showed that the sulfur content can be lowered from 0.1% to less than 0.005% by adding 0.1% Al and 13 kg/t active lime, and the interfacial reaction layer of lime is mainly composed of calcium aluminate, calcium ferrite and calcium sulfide-they are all in fusion state at 1400°C to benefit the diffusion of sulfur. Thus, the sulfur content decreases from 0.1% to below 0.01% if adding 25%CaCO3 and 3%CaF2 with 15 kg/t active lime. In this way, the high-temperature molten iron is the advantageous condition for lime desulfurization.