Abstract: A zero-thickness interface constitutive model that considers cyclic softening and nonlinearity was proposed. Firstly, large-scale cyclic shear tests were conducted on the sand-steel interface to obtain the exponential softening law of strength parameters under cyclic shear. A cyclic softening equation considering the coupling effect of soil relative density and structural roughness was proposed; Secondly, the hyperbolic model incorporating the cyclic softening equation was used as the skeleton curve model to simulate the evolution of the interface from the initial state to the critical state under cyclic loading; Finally, considering the nonlinearity of interface shear, a hysteresis loop model of shear stress-shear displacement was constructed. In addition, empirical formulas for the strength parameters, stiffness parameters, normal stress, relative soil density, and structural roughness of the model were summarized. The newly established model was used to predict the experimental results of this paper and existing literature results, demonstrating its good fitting effect on the interface cyclic shear test.