The shear stress characteristics of the interface between coarse sand and structure were quantitatively analyzed and discussed by using the multifunctional interface shear instrument. The colored sand strips were fixed into a shear box to characterize the movement of sand particles during the tests. The results show that the spatial distribution of shear zone after shear experiment could be reflected by the color sand strips. The thickness of the shear zone formed in the shear experiments are about 6~11 mm, and the thickness of the shear zone increases with normal stress. The spatial distribution of the shear zone is irregular. In the shear direction (X direction), the shear zone exhibits a tendency that shear zone is thick at the central position and thin at both ends of the shear box. The thickness of the shear zone is approximately uniform in the vertical shear direction (Y direction). Under the friction action between particles, the sand particles in the groove drive the sand particles nearby to move together and thus the shear zone is formed during the tests. The dilatancy of sand is caused by the deformation of the sand particles in the shear zone. The dilatancy rate is fast at the initial of the experiment, and then the dilatancy rate slows down after the shear strength reaches the peak.