The invention relates to an ultra-low-sulfur steel smelting method which comprises the following steps: controlling converter charging steel scrap and molten steel conditions; in the KR desulfurization process, thoroughly clearing desulfurization slag in the form of double slagging-off; in the converter process, controlling in-furnace re-sulfurization through material balance; and in the RH process, adding a desulfurization agent for desulfurization again. According to the ultra-low-sulfur steel smelting method, the type of steel scrap is designed to be a finished product of low-sulfur steel scrap with the sulfur content of lower than 0.012%, and the adding amount of the steel scrap is controlled to be 150-170 kg/ton steel; the temperature of molten steel is higher than 1300 DEG C, the content of silicon is lower than 0.4%, and the content of sulfur is lower than 0.03%; a double slagging-off method is adopted for the KR desulfurization process, and the blowing slag removal operation isutilized for the slagging-off process; the sulfur content of steel grades of two furnaces before smelting is required to be lower than 0.020%, and no slag remaining operation is adopted before the production of ultra-low-sulfur steel; the carbon and oxygen product is less than 0.0022; the alkalinity R is controlled to be 2.9-3.3; and in the RH process, the alloying operation is performed 20-25 min after a main valve is opened. The ultra-low-sulfur steel smelting method provided by the invention has the beneficial effects that through the whole-process control, the content of a sulfur component in the molten steel is controlled to be 15 ppm or lower, so that the high requirements for the properties of the steel grades can be met.