Abstract: Rockfill materials are easily broken under external force. Based on the single particle crushing mechanism, the indestructible defect is simulated in particle of rockfill materials depending on the generated particles cluster units to overcome rigid circular particle. A broken numerical model for particle of rockfill materials is established by adopting the linear contact model. Indoor plane strain tests are simulated. The internal contact force, micro crack and a variety of energy changes in rockfill materials are analyzed under the loading process. The breakage mechanism for particle of rockfill materials is investigated. The results show that the numerical sample generated by particle clusters can more truly reflect the breakage of particle of rockfill materials through the internal bond strength fracture. The breakage of particle of rockfill materials occurs first in the large particle size and contact force larger particles, then gradually to direction of the maximum pressure, finally shear fracture sliding plane is generated. The number of shear micro crack is greater than that of tensile micro crack throughout the whole loading process, the particle breakage mainly is shear failure, and a lot of particle breakage is produced near the peak point. The total input energy stores in particle cluster in the form of elastic strain energy under small deformation. The elastic strain energy can be converted to other forms of energy dissipation in the form of storage release under large deformation. The research results can provide reference for the study on the deformation of rockfill dams.