Abstract: The particle breakage phenomenon of coarse-grained soils during shearing has been widely known, and a lot of researches have been performed in the fields of experiments and theories. A series of drained shear tests on rockfill materials with different gradations and densities under different confining pressures are carried out by using large-scale triaxial apparatus, and the particles of rockfill samples before and after tests are analyzed to discuss the particle breakage rules of rockfill materials as well as their influencing factors. The test results indicate that the density has small influence on the particle breakage, while the gradation and confining pressure have great influence on the particle breakage. The larger the confining pressure, the severer the particle breakage. A comparison of grain-size distribution curves of rockfill specimens before and after tests shows that the particle breakage mainly occurs within the range of particles with grain size larger than 20 mm, and the variation amplitude of grain size has a decreasing tendency with the decrease of the grain size. Based on the fractal theory, an expression of relationship between the fractal dimension of particle breakage and the confining pressure and particle gradation is proposed so as to provide a basis for further researches on strength, deformation and dilatancy of rockfill materials.