Abstract: Taking high phosphorus hot metal with w(P)=0.48% as the research object, dephoshporization behavior of CaO-SiO₂-Al₂O₃-Fe₂O₃ slag system at 1 400℃ was studied by high temperature hot state test.The effect of basicity, Fe₂O₃ and Al₂O₃ content on the dephosphorization of CaO-SiO₂-Al₂O₃-Fe₂O₃ slag system was investigated. The results show that with the increasing of slag basicity, the dephosphorization rate of slag system increases at first and then decreases slightly, mainly because the introduction of O^2-and Ca²⁺ promotes the formation of PO₄^3-complex ion and Ca²⁺-PO₄^3-weak ion pair. With the increase of Fe₂O₃ content, the dephosphorization rate of slag system increases gradually. Fe₂O₃ in slag accelerates the melting rate of CaO, and improves the oxidation of slag system, thus improving the dephosphorization ability of slag system. When the w(Al₂O₃) is 1%-3%, the dephosphorization rate of slag system maintains at about 77%. With the further increased of Al₂O₃, the dephosphorization rate of slag system decreases gradually. The main reason is that Al₂O₃ changes the proportion of liquid phase in the slag, and then affects the mass transfer process of dephosphorization reactants and products between slag and molten.