Abstract: Studying on the Ca O base containing V₂O₅and Ti O₂semi-steel slag, a model of enrichment degree R_ci-cjwas built with the help of the ion and molecule coexistence theory, the result was compared with the actual enrichment form of phosphate.The results indicate that with the increasing of basicity, the mass action concentration of 3CaO·P₂O₅gradually decreases, and the mass action concentration of 4CaO·P₂O₅gradually increases.While the mass action concentration of 2CaO·Si O₂first increases and then decreases.The enrichment possibility range of the C₃P+C₄P is 87%-94%and the C₂S that is the essential substance for the formation of the rich phosphate mineral phase is main calcium silicate compounds.The solid solution 2CaO-Si O₂-3CaO-P₂O₅ (C₂S-C₃P) and 2CaO-Si O₂-4CaO-P₂O₅ (C₂S-C₄P) are the primary phosphate enrichment phase in the slag.According to the scanning electron microscopy (SEM) results, X-ray diffraction (XRD) analysis and hypothesis, the containing P₂O₅solid solution in dark grey area is calculated as2CaO·Si O₂-3CaO·P₂O₅and 2CaO·Si O₂-4CaO·P₂O₅, which is consistent with the theoretical calculation results.