Abstract: The shear properties of the interface between the underlying foundation and soil are very important for the safe construction of the entire structure. Sandy soil layers are common in the upper soil layer of the foundation, and the particle size of sand and surface roughness of the foundation will affect the mechanical properties of the pile foundation. It is very important to study the shaft resistance of the sand strata. In order to investigate the interface shear strength, interface shear strength index with different particle sizes of sands, different roughnesses and different normal stresses, the interface shear tests on sands having particle sizes of 0.075~0.150 mm and 0.150~0.300 mm with rough steel plate and concrete plate are performed by using an improved direct shear apparatus. The testing results indicate that the interface shear stress-displacement relationships can be described by a hyperbolic model. The ratio between the peak shear stress of the test and the peak shear stress of the model ranges from 0.85 to 0.95. The peak value of the measured shear stress increases with normal stress and roughness. The peak shear stress of the particle size Ⅰ is slightly larger than that of the particle size Ⅱ. The peak shear stress of the interface between concrete and sands is larger than that of the steel-sands interface. The shear surface for the sand-structure interface without engraved lines is a moving horizontal plane, while the shear surface for the sand-structure interface with engraved lines is composed of discontinuous horizontal shear planes and dynamic curved shear surfaces. The interface friction angle increases with roughness. The shear strength index of the particle size Ⅰ is slightly larger than that of the particle size Ⅱ. The friction angle for the sand-steel interface ranges from 23° to 28°, and the friction angle for the concrete-steel interface ranges from 25° to 31°. The research and analysis results can provide an experimental reference for shaft resistance estimation and numerical simulation of the sand strata.