Phosphate rock is a vital nonrenewable resource. In order to find new source of phosphorus, the recovery of phosphorus from dephosphorization slag produced by duplex steelmaking process (De–P slag in De–P_De–C steelmaking process) was investigated in the present paper. It was demonstrated that the P-rich phase in dephosphorization slag is difficult to recover effectively by magnetic separation as the reason of P enriched phase inlay in the Fe enriched phase in the slag. The relationship between P recovery ratio and magnetic intensity and slag particle size were also obtained. A series of slag modification experiments were designed to investigate the recovery of phosphorus from high P₂O₅ content dephosphorization slag produced by duplex high phosphorus hot metal refining. It was found that the addition of SiO₂, Al₂O₃ and TiO₂ has a positive influence on the P recovery ratio. However, the P recovery ratio and the concentration of P₂O₅ in unmagnetized slag showed a reciprocal relationship with increasing SiO₂ and Al₂O₃ content. The P recovery ratio was little affected by the addition of Fe_tO and MnO. Furthermore, the P recovery ratio increased under the stirring condition. 74% and 87% P were recovered in the unmagnetized phases with adding 10% SiO₂ and Al₂O₃, respectively. The results demonstrated that most of the phosphorus in the slag could be recovered through slag modification and magnetic separation.