Abstract: To effectively separate P from steelmaking slag and achieve the co-treatment of industrial wastes, the modification of molten steelmaking slag by LF slag is proposed, and then the P-bearing Ca₂SiO₄ is separated by selective leaching. The effects of modification treatment, pH value, steel slag particle size, and solid-liquid ratio on the leaching behavior of each element are studied. The result of research shows that after LF slag modification, the mass fractions of Ca₂SiO₄ and Ca₂Fe₂O₅ phases increases, while that of RO phase decreases. LF slag modification increases the leaching ratio of P from slag, and suppresses the dissolution of Ca and Al, beneficial for the selective leaching. Decreasing the pH of the leachate enhances the leaching ratios of each element but results in the dissolution of a part of Fe at a lower pH value. At pH=1.5, the leaching ratio of P from modifies slag is approximately 85%, while that of P is less than 9%, achieving a better selective leaching. With the increase of slag particle size, the leaching ratios of Ca, Si, and P decreases. In the case of a high solid-liquid ratio, most of the P and Si could be separated from the modified slag.