Abstract: In order to study the relationship between particle breakage and dilatancy characteristics of rockfill materials under different porosity and stress conditions, the large-scale triaxial tests are carried out on the rockfill materials of a high rockfill dam. The results show that the of rockfill materials with different porosities exhibit different degrees of dilatancy under low confining pressure. As the confining pressure increases, the dilatancy phenomenon of the rockfill materials gradually disappears and turns into shrinkage. Therefore, the concept of breaking dilatancy ratio is put forward and used to describe the relationship between particle breakage and dilatancy characteristics. It is found that as the crushing rate of rockfill particles increases, the breaking dilatancy rate decreases in the form of a power function, and the dilatancy phenomenon gradually disappears. As the initial porosity of the rockfill materials increases, the failure dilatancy decreases, but the larger the confining pressure, the less the initial porosity has a smaller effect on the dilatancy characteristics. Based on the above test results, the relationship among the initial porosity of the rockfill materials, their dilatancy and particle breakage is established to predict the dilatancy of the rockfill materials under different confining pressures.