The cryogenic grinding performance of scrap tire rubber modified by devulcanization treatment in supercritical carbon dioxide (ScCO2) was studied with a fluidized-bed jet mill. Scrap tire rubbers devulcanized with various concentrations of devulcanizing reagents were ground to analyze the effect of the degree of devulcanization on the particle size distribution of the ground product. Population balance modeling based on selection and breakage functions was adopted to explore the evolution rule of the particle sizes in the grinding process. The results of the cryogenic grinding experiment show that the devulcanization treatment can promote particle size reduction and lead to the transformation of the grinding mechanism from abrasion to cleavage or fracture. Furthermore, Kapur function fitted by the population balance modeling was proposed with a cubic polynomial, and the calculation results agreed well with the experimental data. (C) 2020 Published by Elsevier B.V.