Abstract: The deformation behaviors of coarse granular materials under three-dimensional stress state are crucial to the settlement of earth-rockfill dams. A series of tests under constant minor principle stress and constant coefficient of intermediate principle stress are conducted by the large-scale true triaxial test system. The test results show that the dilatancy of coarse granular materials is quite strong when the minor principle stress is small. The contraction of coarse granular materials is enhanced when the minor principle stress increases. The dilatancy becomes weaker when the coefficient of the intermediate principle stress increases from 0 to 0.5. But the dilatancy becomes a little bit of stronger when the coefficient of the intermediate principle stress increases to 0.75. The major principle strain behaves as contraction and the minor principle strain shows as dilatancy in all the large-scale true triaxial tests. The intermediate principle strain is compressed under the normal three-dimensional stress state. However, the dilatancy occurs in the direction of the intermediate principle stress under the conventional triaxial stress state.