The coarse aggregate can show significant particle breakage characteristics under external force loading. Studying the particle breakage process is one of the research focuses at present. Based on one coarse particle failure mechanism, a numerical model for particle breakage is developed, in which the nonlinear contact H-Z model and a density-control method are introduced and the variation of a single particle breakage strength and diameter are considered. Based on the proposed model, the biaxial shear test of coarse aggregate is carried out and compared with the laboratory test results. It is shown that the proposed particle breakage numerical model can describe well the relationship between deviatoric stress and axial strain, and the relationship between volume strain and axial strain. The particle breakage ratio obtained by numerical simulation is consistent with the results obtained by laboratory test. The normalized particle breakage ratios under different confining pressures are practically coincident, and can be fitted by a hyperbolic curve function without considering particle breakage in sample preparation and consolidation processes. As the confining pressure increases, the particle breakage ratio increases, and the final grading curve of sample coincides with that proposed by Einav, which has a fractal dimension of 2.6.