Abstract: During the dredger filling process of island reefs, a layered foundation of coral sand and coral gravel will be formed.We investigated the bearing characteristics of pure sand, pure gravel homogeneous foundation and sand-gravel interlayer foundation with different layer thickness ratio by indoor model tests.The test results showed that the bearing capacity and deformation modulus of pure sand foundation increased with the relative density, and the bearing capacity of dense foundation was obviously higher than that of medium dense foundation; the bearing capacity and deformation modulus of pure gravel foundation were more than twice of that of pure sand foundation under the same relative density; the bearing capacity of upper gravel and lower sand foundation increased with the increase of gravel layer thickness, and the gravel layer had a certain stress diffusion effect, and the larger the thickness, the more obvious the stress diffusion.The bearing capacity of upper sand and lower gravel foundation increased with the decreasing of gravel layer depth, and the lying gravel layer under the foundation can weaken the stress concentration at a certain depth in the foundation, the shallower the depth, the greater the weakening degree.The test results are of great significance for determining the natural bearing capacity of sand and gravel interlayer foundation and the selection of bearing layer.