The invention provides a mild steel desulphurization refining method with high desulfurization rate and stable desulphurization effect. The method provided by the invention comprises the following steps of: carrying out tapping of molten steel smelted from a converter to steel ladle, and respectively adding alloy and desulphurization refining slag into the molten steel in the steel ladle during the tapping process for molten steel alloying and desulphurization slagging, wherein a slag modifier is added into the ladle slag formed in the steel ladle after the tapping process. By the adoption of the method provided by the invention, oxygen in the molten steel can be effectively removed, oxidability of the ladle slag can be reduced, properties and composition of the ladle slag can be improved, desulfurization efficiency of the molten steel can be greatly improved, and molten mild steel refining desulfurization rate can be ideally and stably controlled within 30-60%, and fluctuation of the sulfur content in finished steel can be minimized. In addition, the content of non-metallic inclusions in the molten steel can be decreased, and purity of the molten steel can be raised.