Abstract: Al₂O₃ and solid calcium aluminate were considered as un-reacted cores, the diffusion of aluminum cations in the liquid calcium aluminate layer was confirmed as the rate determining step of Al₂O₃ inclusion modification, and further a kinetic model of Al₂O₃ inclusion modification was established on the basis of the un-reacted core model. The model parameters were calculated by thermodynamic analysis. Modelling results show that the time of Al₂O₃ inclusion modification to completely liquid calcium aluminate will be much longer when the size of Al₂O₃ inclusions increases. Moreover, increasing the Ca content in a reasonable range is beneficial not only to modify Al₂O₃ inclusions to liquid calcium aluminate from thermodynamics but also to speed the modification process whereas the enhancement weakens when the Ca content exceeds a critical level. Temperature rise is disadvantageous to Al₂O₃ modification chemical reaction so the driving force of Al₂O₃ inclusion modification decreases correspondingly, namely temperature rise is not so obvious to speed Al₂O₃ inclusion modification. Finally, the kinetic model results were verified by industrial trials and they accord with each other very well.