This paper analyzed the constitutive relationship of soil-structure interface，studied the deformation characteristics and stress paths of interface under different normal stresses with laboratory direct shear test，and established a mathematical model reflecting the constitutive relationship of soil-structure interface. The test results show that normal stress and interface roughness are the main factors affecting the shear characteristics of the interface. The shear failure mode of the interface changes due to the existence of consolidation stress. Its value is related to the roughness of the interface and the shear properties of the soil. Moreover，we proposed an improved statistical damaging model considering the whole shear process of the contact surface，based on ignoring the thickness of the interface and combining with the “three-stage” mode of the shear process. The correctness of this improved model is verified by experimental data. Moreover，this model can reflect the global deformation around the soil-structure interface under certain normal stress.