Abstract: The rheological properties of rockfill are studied based on the time-dependent behaviors of particle breakage. Firstly, a microscopic rheological model for rockfill is established based on the theory of sub-critical expansion of cracks. Secondly, the reasonable crushing modes of particles are analyzed. Macro-time is calculated by means of the method of the two-step circulation decision, and the relevant programs of particle flow are compiled. Finally, a series of numerical tests are carried out in order to simulate the uniaxial numerical rheological tests based on the selected micro-parameters. The simulated results are partially compared with the laboratory experiments, and good agreement is achieved. The results and analysis show that the modes of particle breakage have influence on the simulated results, that is, the closer to the real particles, the better the simulated results. The magnitude of rheological deformation is mainly dependent upon the breakage of instantaneous particles, which is caused by the larger contact forces. The rheology results from the delayed breakage of particles induced by the extension of microscopic cracks.