Abstract: A large-scale simple shear test device with staged shearing rings is developed. A series of simple shear tests are conducted on two different rockfill materials with different particle compressive strengths under different vertical stresses and large shear deformations. Changes of particle breakage during compression and simple shearing are investigated. The results show that the particle breakage relates with the compressive strengths of particles and the applied vertical stresses. The lower the particle compressive strength is and the higher the vertical stresses are, the larger the particle breakage takes place during the compression and the simple shearing process. The particle breakage may tend to a critical value either during the compression or the shearing process. The particle breakage mainly occurs in the process of the confined or shearing compression.