Abstract: During periodic rise and fall in reservoir water level, the state of rockfill materials shows a basically constant deviatoric stress and a cyclic change in spherical stress. To investigate the deformation characteristics of rockfill materials under cyclic loading of spherical stress, a series of triaxial tests under the stress path of low-speed cyclic variations in spherical stress are conducted in this study by increasing or decreasing this stress through controlling pore water pressure. Results show that volumetric strain is increased with the decreasing spherical stress, and decreased with the increasing spherical stress. Generally, with cyclic times increasing, the materials show a trend of volume shrinkage, but the cumulative volumetric strain changes little. The development in shear strain is significantly affected by stress conditions. Effective shear strain increases slowly or increases suddenly in the first cycle times when spherical stress is reduced, while it increases slowly when effective spherical stress is increased. Cumulative shear strain is related to the initial stress ratio and the dynamic stress ratio during the test. The materials may likely have a “state-turning line” that is similar to the critical state line and falls below it. The state of a material will change significantly when its stress lies in the zone between this “state-turning line” and the critical state line.