Due to the weak shear strength of the interface between geomembrane and sand, instability failures in geotechnical structures often occur along this interface, particularly under seismic excitation. The cyclic shear behavior of geomembrane-sand interface has been primarily investigated through laboratory tests. However, the microscale interactions and mechanisms occurring at the interface have not been explored. Therefore, this paper focuses on the cyclic shear behavior of geomembrane-sand interface from a microscale perspective using the discrete element method (DEM). The sand is modeled as spherical particles with a frictional contact model incorporating rolling and twisting resistance to account for the shape effect and particle crushing. The geomembrane is reproduced through an overlapping technique with the parallel bond model (PBM). Micromechanical parameters of both materials and their interface are calibrated based on laboratory data. Results demonstrate that the DEM simulation effectively capture the strain-softening behavior of the interface under cyclic loading. Furthermore, the microscale cyclic shear behavior of smooth/textured geomembrane-sand interfaces is studied in terms of coordination number, interlocking level, force chain evolution, and soil fabric changes.