Abstract: This paper proposes a constitutive model for soil-structure interfaces by combining the tangential stress-strain relation and normal stress-strain relation of contact surface soils. Based on the analysis of the deformation properties of the soil-structure interface and the shear slip plane of the soil on the interface corresponding to octahedral surfaces under unit body 3D stress states, the tangential stress-strain relation is established by applying the 3D elastoplastic constitutive model for soils to the octahedral surface. The normal compressive deformation of the soil on the interface is similar to that of side-limit condition. Therefore, the normal stress-strain relationship of the soil on the interface is established on the basis of the loading-deformation relation under the side-limit condition. The proposed constitutive model has only four material parameters with clear physical meanings. These four parameters can be determined through the isotropic compression test and the conventional triaxial compression test. Comparisons between the proposed constitutive model and test results of the soil on the interface indicate that the model is capable of reasonably describing the tangential softening and hardening characteristics and normal deformation rules of the soil on the surface. Furthermore, the proposed model is integrated in the general finite element package ABAQUS via FRIC to simulate the deformation process of the soil on the interface. The simulations show that the FRIC subroutine is able to reflect the nonlinear mechanical behavior of the soil-structure interface.