Abstract: The phosphate rock powder from Hebei province is dry-milled by a planetary ball mill.The particle morphology, crystallinity, specific surface area and surface free energy of the grinding products at different grinding time are investigated.The variation law of the phosphate rock properties in the process of ultrafine grinding and its relationship with the solubility ratio of phosphorus ore in citric acid is systematically analyzed.The results show that the coarse-grained phosphate rock is gradually pulverized into fine particles while the degree of crystallinity of the apatite in the phosphate rock is significantly reduced, thus the amorphous form is increased, with the grinding time extending from 0 min to 180 min.Meanwhile, the specific surface area and surface of the phosphate rock are increased, which increase from 0.67 m²/g and 24.08 mN/m to 5.06 m²/g and 38.69 mN/m, respectively.The specific surface area and surface free energy of phosphate rock are positively correlated with the enthalpy solubility ratio of phosphorus ore in citric acid, and the solubility ratio of phosphorus ore in citric acid increase significantly from 9.14% to 61.68%.The above research results provide certain significance for enriching the theoretical basis of phosphate rock powder activated by ultrafine grinding.