Abstract: Aiming at the shear-seepage problem on the interface between the contact clayey soil and the concrete base at the bank slope of a high clay-core dam, a new complete set of shear-seepage test system for clayey soil-structure interface is developed to investigate the mechanical and seepage characteristics of the interface between clayey soil and structure. The test system can produce large shear deformation on the interface, control the orthogonality of the shear deformation and the seepage direction, and automatically obtain the evolution process of mechanical and seepage characteristics of the interface. The compacted clayey soil permeability tests and the mechanical tests on the contact clay-structure interface are carried out to verify the reliability of the test system. The shear-seepage coupling tests are conducted on the contact clayey soil materials of the core wall earth-rock dam. The results indicate that under low normal stress, the permeability coefficient decreases first and then increases with the increase of shear deformation, and finally stabilizes. The permeability coefficient at stability does not exceed the initial permeability coefficient. While under high normal stress, the permeability coefficient decreases continuously and reaches stability with the increase of shear deformation. The influence mechanism of soil dilatancy on the permeability of contact clayey soil-structure interface under different normal stresses is discussed. It is proposed that the influences of structure roughness on the permeability characteristics of the interface need further studies.