The utility model relates to a molten iron desulfurizing device, which comprises a foundry ladle, a top blowing gun, a dual-yarn feeding machine, a slag digging machine, a slag basin, an air permeable brick, and an air inlet pipe. The utility model is characterized in that the bottom of the foundry ladle (1) is provided with the air permeable brick (6) and the air inlet pipe (7); a core-spun yarn which is fed by the dual-yarn feeding machine (3) is a magnesium-calcium core-spun yarn (8). The molten iron desulfurizing device does not need to build up a special workshop and facility and has the advantage of simple operation. The desulfurizing rate of the molten iron desulfurizing device is not less than 60 percents. Building up a molten iron desulfurizing device with a processing ability 1000000 ton every year, the utility model only needs 3 percent of the cost of building up a molten iron desulfurizing station. The utility model also has the advantages of no pollution, no dust, and operation environment improvement.