In order to analyze the interface shear strength-shear displacement curve of expansive clay under different water content and different normal stresses, the influence of water content on the mechanical properties of the expansive soil-concrete interface was studied through the indoor expansive soil-concrete interface. The results show that the stress-strain curves under different water content conditions have no strain-softening phenomenon, which basically conforms to the strain-hardening model. The increase in water content has a more obvious deterioration effect on the shear strength of the interface, and the peak value of the stress-strain curve also lags behind. The interface shear strength and normal stress of the same water content are in good agreement with the Mohr-Coulomb strength criterion. With the gradual increase in water content, the interface shear strength also shows an decreasing trend. The cohesion of the interface increases first and then decreases gradually. The equivalent shear modulus of the interface shows a downward trend. At the same time, the change rule of interface strength caused by interface cohesion and interface internal friction angle was analyzed by microscopic angle. With the increase of water content, the internal friction angle of the interface gradually shows an inversely proportional function decreasing trend. The interface friction coefficient was introduced to further analyze the mechanical properties of the interface friction. At the same time, the great influence of interface cohesion and normal stress on the interface friction was corrected. For the friction estimation of shallow slope soil and pile foundation, it is reasonable to consider the influence of normal load on the interface friction coefficient.