Abstract: The dynamic shear characteristics of the liner interface have significant impacts on the seismic stability of landfills. However, the existing interface dynamic constitutive theory cannot fully reveal the evolution mechanism of the physical state during the dynamic shear process of a liner interface. The dynamic shear process of geomembrane/GCL interface is divided into two stages: deformation of soil materials and sliding friction of interface. The concepts of critical state and critical stress of interface, triggering interfacial physical state evolution, are proposed. Considering the basic laws of interfacial dynamic shearing, the elastic-visco model and friction coefficient model are utilized to describe the two stages. The accuracy of the interfacial dynamic model is verified by geomembrane/GCL interface dynamic shear tests under multiple cycling conditions. The research exhibits that the proposed model can effectively simulate the mechanical properties and physical state evolution of the dynamic shear deformation of a liner interface, providing a theoretical support for a seismic stability analysis of landfills.