Abstract: The distribution of phosphorous in bulk slag, inside and outside the 2CaO · SiO2 in the molten CaO-SiO2-FetO-P2O5 slag was investigated. The research results showed that the existing 2CaO · SiO2 solid particles are the condensation sites for the phosphorous enrichment. The enrichment process of phosphorus in the molten slag can be considered as the three substeps: (1) the mass transfer of phosphorus from bulk slag to the surface of 2CaO · SiO2 particle; (2) the formation of 2CaO · SiO2-3CaO · P2O5 solid solution on the surface of 2CaO · SiO2 particle by solid solution reaction, and (3) the diffusion of phosphorus from the product layer of solid solution to the inner of 2CaO · SiO2 particle. Higher temperatures accelerate the phosphorous enrichment. Comparing to the larger 2CaO · SiO2 particles, the completion time of phosphorous enrichment is shorter for the smaller particles, but the larger ones are favorable to the separation of phosphorus-rich phases from bulk slag.