Abstract: A metallurgical method for refining grains of steel includes adding aluminum into molten steel obtained from a secondary refining process. Aluminum reacts with oxygen and sulfur in the molten steel to reduce the total oxygen content in the molten steel to 15-120 ppm, to reduce a sulfur content in the molten steel to 15-150 ppm, and to produce aluminum oxide, obtaining cleaner molten steel. Magnesium is added into the cleaner molten steel and reacts with oxygen, sulfur, and aluminum oxide in the cleaner molten steel to reduce the total oxygen content in the molten steel to 10-60 ppm, to reduce the sulfur content in the molten steel to 5-100 ppm, and to produce inclusions including magnesium oxide, magnesium sulfide, and magnesium-aluminum spinel. Precipitates of the inclusions can serve as crystalline cores in a subsequent crystallization process to obtain fine-grained steel.