Abstract: The normal operation of concrete face rocfill dam (CFRD) depends mainly on the stress-strain behaviour and safety of the concrete face. The mechanical properties of concrete face are significantly different from the gravel underlayer. The contacting situation between both materials, i.e., the interface behavior, is consequently a crucial factor influencing the stress-strain state of the concrete face under self-weight and huge water pressure of reservoir. The study on interface behavior drew much attraction for the safety design of CFRD. Interface shear test was carried out. But the test apparatuses were commonly limited in geometrical scale relative to actual gravel particle size in construction. The interface shear test remained as an interesting problem to make clear understanding about the interface properties. An up-to-date largest simple shear apparatus was developed to perform the interface shear test for a CFRD (Shuibuya Dam) being constructed in China with the height of 233m. By means of the new apparatus, three types of interfaces were tested, including ①face-gravel direct contact; ②face -gravel indirect contact with face protected by thin cover of cemented sand; ③face-gravel indirect contact with face protected by thin cover of emulsified asphalt. The test results provide some important insights about the interface properties.