Abstract: The steel piles and steel suction caissons are widely used in ocean engineering, in which the mechanical behaviors of the interface between soils and foundations determine their bearing capacities. A series of saturated sand–steel interface drained shear tests are conducted to reveal the effects of the grain size distribution, surface texture and normal confinement conditions on interfacial shear behaviors. The research shows that due to the differences in the shear mode of sand particles and the dissipation of the pore water pressure, the shear stress-displacement curve under a constant normal load (CNL) experiences an obvious strain-softening phenomenon, whereas the maximum shear stress increases with the increase of the normal stress increment under a variable normal load (VNL). For the smooth and convex surfaces, the interfacial friction angle increases linearly with the increase of C_u. For the groove surfaces, the interfacial friction angle decreases with the increase of C_u. The shear efficiency of the saturated sand-steel plate interface is greatly influenced by water, and the presence of the water film weakens the friction between sand particles and steel plates, thus, the maximum efficiency cannot be developed on interfaces.