Abstract: The rockfill material crushes during the process of rheology and the fractal dimension of rockfill material varies with time. Based on the basic rule of rheological process of coarse-grained soils, the fractal theory is applied into the analysis of rheological process, and two typical expressions of fractal dimension that varies with time are given. The reationship between the particle breakage index and the fractal dimension is also described. By analysing the particle breakage index of incomplete rheological test, the reasonability of the expression of hyperbola fractal dimension during rheological process is confirmed. On this basis, the volumetric strain is derived considering the energy balance of coarse granular aggregates and the related research of the particle breakage energy. Thus a rheological constitutive model for rockfill materials is proposed. Compared with experimental data, the proposed model can reflect the rheological properties of rockfill material based on fractal theory.