Abstract: Al addition can not only promote the desulfurization by deoxidation in the hot metal, but also improve the kinetic conditions of desulfurization with lime. To reduce the cost of desulfurization treatment, theoretical and experimental studies have been conducted for hot metal desulfurization with composite reagent of calcium oxide and aluminum. The experiment results show that, with the addition of a certain amount Al in CaO-based desulfurizer, the desulfurization rate can be improved. With 5 g/kgFe Al addition, the desulfurization ratio can be increased by 31.4%. With 0.6 g/kgFe Al addition, the sulfur content in hot metal can be reduced to below 0.02% within 20 min. The rate constant of desulfurization reaction was also calculated for different amounts of Al addition.