Abstract: The filling characteristics of rockfill materials are closely related to their mechanical properties. They can be changed by particle breakage, which is one of the main factors of the scale effect of rockfill materials. It is of great significance to further understand the complex mechanical response and mechanism of scale effect from the perspective of filling properties. A series of numerical triaxial compression tests considering different particle breakage strengths are taken to study the influence of particle breakage on the scale effect of filling characteristics of rockfill materials, and the mechanism of the scale effect is further revealed. It is found that the lower the particle breakage strength, the more obvious the scale effect. The particle breakage has obvious influence on the macro- and micro-parameters of filling characteristics. The porosity decreases with the increasing sample size before and after compression tests, which is more significant with the lower particle breakage strength. The effective porosity of samples with the same size after compression tests decreases with the lower particle breakage strength. The effective porosity of samples before compression tests increases with the increasing sample size, which is opposite to the trend after compression tests. During the process of compression tests, the larger samples produce more mechanical unstable particles than smaller ones, which is one of the reasons for the scale effect of rockfill materials.