The invention discloses a method of optimizing converter slagging. According to weight percentages, compositions of refining slags comprise 40%-60% of CaO, 15%-35% of Al2O3, less than or equal to 10% of Si, less than or equal to 5% of TFe, 5%-15% of Mg, and the balance impurities brought by slagging raw materials. The processing steps comprises: (1) materials are recycled; (2)slag charges are added; (3)an oxygen blast system is adopted; and (4) a slagging system is adopted. Aiming at the production line of short process of the converter continuous casting, alkalinity in the smelting process is improved by recycling casting residues and utilizing effective calcium oxide in the casting residues, and converter slags are modified by utilizing Al2O3 in the casting residues, the melting point of the converter slags is reduced, the slagging effect in the smelting process is ensured, slagging in the whole process is ensured, and splashing is reduced, so that the dephosphorization rate is stabilized and the steel consumption is reduced. The method of optimizing converter slagging is suitable for converter smelting of low-carbon steel, medium-carbon steel and high-carbon steel; the existing apparatuses do not need to be renovated; and on the basis of not increasing the investment and production cost, the dephosphorization rate of a converter is improved by optimizing the technology, and the index value of steel is reduced.