Abstract: Principle and feature of combined blowing process of lime to magnesium for desulfurization of hot metal are briefly introduced, and the effect of ratio of lime to magnesium powder 2. 0 ~ 3. 5 ： 1, 3.5 ~ 5. 0 ： 1 and 5.0 ~ 6.5：1 on end sulfur in metal, resulphurization rate, iron loss and temperature drop in blowing process, desulphurization time and 120 t BOF steelmaking results are commercial-tested. It is obtained that with using the ratio of lime to magnesium powder 3. 5 ~5. 0 ： 1, the resulphurization amount is less than 0.003 5% , the iron loss is less than 26 kg/t, temperature drop is less than 18 ℃ and the yield of steel liquid is more than 87% , so the production cost decreases markedly.