The meltability of desulfurizer in molten iron affects the desulphurization efficiency directly,the better desulfurizer compositions are obtained by measuring the melting performance with different ingredient of desulfurizer,which provides a reference for industrial production of magnesium oxide based desulfurizer.The results show that the desulfurizer has bad fluidity which makes it difficult to desulfurate. The melting property has no obvious changes with the addition of CaF2,while B2O3 as the addition can change the melting performance of desulfurizer obviously. The melting temperature of desulfurizer is decreased and the fluidity is improved.The desulfurizer can meet the requirements of hot metal pretreatment,and the best additive amount is 2% of original amount.