Abstract: Theoretical calculations by FactSage software and melting experiments were performed to systematically study the melting temperature characteristic of a CaO-FeO-Al₂O₃-SiO₂ fluoride-free slag system used for hot metal dephosphorization pretreatment. Three influence factors of the melting temperature of the slag were researched which were the slag's binary basicity, the mass fractions of Al₂O₃ and FeO. The results show that the mass fraction of FeO has the greatest impact on the melting temperature of the slag among three factors. The obtained best proportion of the slag is the binary basicity of 5.5, 10% Al₂O₃ and 45% FeO. Under the experimental conditions, the melting temperature characteristic of the optimal slag can meet requirements for hot metal dephosphorization pretreatment.