Abstract: Consulting a practical dephosphorization slag in the converter, samples with different levels of F, P₂O₅, FeO, MgO and basicity were prepared in laboratory, and the effect of composition on their solubility in citric acid was analyzed by chemical analysis methods. The results show that when the slag contains fluorine, P and F mainly form fluorapatite, and the solubility in citric acid of the slag sharply decreases when the fluorine content increases in the slag. if there is no any fluorine in the slag, the solubility in citric acid can be reached up to 92.5%, but when the mass fraction of fluorine in the slag reaches to 0.5%, the solubility in citric acid drops to less than 50%. The solubility in citric acid is improved with the increase of basicity, for increasing Ca²⁺ can destroy the Si-O network structure. With the increase of MgO content, the solubility in citric acid increases since in the process of cooling, Mg²⁺ inhibits the precipitation of β-Ca₃(PO₄)₂ crystals in which P can not be dissolved easily in the 2% citric acid. The solubility in citric acid decreases with the increase of P₂O₅ content, for P⁵⁺ is formed as PO₄^3- complex ions with O^2-, P⁵⁺ locates in intensive gaps formed by O^2-, and the complex ions can not dissolved easily in the 2% citric acid. The solubility in citric acid will be decreased with the increase of FeOn.