Abstract: Accurate prediction of the evolution law of particle breakage during loading process is of great significance to building the constitutive model for coarse-grained soil. The reasonable definition and accurate calculation of particle breakage indices are the guarantee to exactly study the evolution law of particle breakage during loading process. The fractal breakage index of Einav is introduced and considered as the most suitable one to compare and evaluate the breakage degree of coarse-grained soil among breakage indices. It is realized to accurately calculate the fractal breakage index by replacing fractal gradation equation with the gradation equation for continuous gradation soil. On this basis, the evolution law of particle breakage of coarse-grained soil is studied by selecting the experimental data in the existing literatures. A mathematical model is established to describe the relationship among particle breakage indices, shear strain and average normal stress during triaxial shearing, and the applicability of this model is validated.