In the current state, the numerical computation and structural analysis of earth-rock dam impermeable structure present shortcomings. In this paper, we modified and improved the traditional Finite Element Method (FEM) model by using a new linkage unit to simulate the interfacial shear characteristics between the lower cushion and geomembrane. Additionally we improved the geomembrane finite element analysis accuracy without additional FEM overall size, which can greatly improve the computational efficiency. We successfully simulated the geomembrane force-deformation characteristics at anchoring points for the possible anchoring effect of geomembrane impermeable structure around dam face through adding three-dimensional spring unit at anchor points. The results show that impermeable geomembrane at the top of earth-rock dam face suffered smaller tension, but at the anchoring points at the bottom, it suffered lager tension, so it is prone to tensile crack.