Abstract: Through lab dynamic tri-axial tests on rockfill materials, the characteristics of particle breakage and its influence factors under cyclic loadings are studied. Considering the variable quantity of different ranges of particle size after grain crushing, the particle breakage form of rockfill is differentiated as angular crushing and skeleton crushing in view of the roles that the rockfill particles play in the mixture for the first time. Incorporation with the fractal theory, the broken rate of rockfill is defined as the variable of the fractal dimension of aggregate gradation, which can be obtained by the fractal dimension of aggregate gradation before and after particle breakage. Furthermore, the relationship among the broken rate, the shear strain and the dynamic volume change of rockfill materials is established.