Abstract: The sandstone, limestone, slate are used to simulate the ball-ball normal contact of coarse-grained soil by employing the rock rheological testing system. The breakage process and morphology of particles, elastic core and force-displacement curve are used to analyze the influences of compressive mechanism and breakage characteristics of particles by considering the properties and particle sizes of materials. Through the experimental study, it is found that under the normal contact force, the local breakage occurs firstly at the contact area of the particle, thereafter the elastic core is formed, and the entire breakage of the particle occurs finally after crack coalescence. By data fitting, the breakage criterion for spherical particles and empirical formulae for elastic core sizes are established respectively. The mechanism of particle breakage is revealed from the perspective of particle contact of coarse-grained soil, and it opens up a new way to study the particle breakage of coarse-grained soil. It can also provide contact mechanic parameters directly for discrete element numerical simulation.