The invention provides a high-strength sulfur-oxygen nucleating agent. The high-strength sulfur-oxygen nucleating agent comprises the following elements in percentages by mass: 70-76% of Si, 0.2-1.0%of Ca, 0.3-0.5% of Ba, 1.5-2.0% of La, 0.5-1.5% of Al, 0.3-0.9% of S, 0.3-0.9% of O, 0.5-1.5% of Sb and the balance of iron. The sulfur-oxygen nucleating agent is prepared from the following raw materials in parts by weight: 2-4 parts of steel scrap, 130-140 parts of silicon iron, 1-1.4 parts of silicon barium, 1-1.8 parts of calcium silicon, 2-4 parts of pure lanthanum, 1.5-2.5 parts of stibonium, 1-2 parts of FeS and 1-1.4 parts of FeO. By the prepared high-strength sulfur-oxygen nucleating agent, the number of graphite nodules in nodular cast iron can be increased obviously, the strength and toughness of the nodular cast iron can be improved, the chilling tendency of the nodular cast iron is relieved obviously, the nodularity, the number of graphite nodules and the number of ferrites ofthe nodular cast iron are increased, shrinkage in a casting process is eliminated, and complicated castings with excellent quality can be formed.