Abstract: This is a paper in the field of mineral processing engineering. Application of ultra-fine grinding technology to treat phosphate ore can change the physical and chemical properties of phosphate containing minerals in phosphate ore, thus improving the dissolution and release of phosphorus in phosphate ore, so that it can be used as phosphate fertilizer. As an ultra-fine grinding equipment, the feasibility of using stirred mill to treat phosphate ore and the research on the influence of process parameters on grinding effect are not perfect. A phosphate ore in Hebei Province was wet ground by a vertical stirring mill in this paper.The particle size distribution of the ground product was detected by NKT6100-D laser particle size analyzer.The effect of grinding process parameters on the particle size composition of product and the content of newly formed particles was explored, and the product particle size was parametrically analyzed by R-R equation to determine the more appropriate operating process parameters. The results showed that under the conditions of agitator speed of 550 r/min, grinding concentration of 65%, filling rate of 60%, feed to ball ratio of 0.5 and grinding time of 30 min, the available phosphorus content and phosphorus solubility in citric acid of 8.75% and 74.03%, particle characteristic parameter b of 0.371 and uniformity coefficient n of 1.426 were obtained. It can be seen that it is feasible to use a vertical stirring mill for ultra-fine grinding of phosphate ore.