According to the seepage characteristics of anti-seepage body of composite geomembrane used in earth-rockfill dam, in combination with an engineering example, the paper used three-dimensional finite element method to simulate the deformation and stress behaviors of composite geomembrane, and analyzed the effect of different heights of earth-rockfill dam on stress deformation of anti-seepage inclined wall built by composite geomembrane. The results show that comparison with low earth-rockfill dam using composite geomembrane, with the increase of dam height, not only the stress and strain of composite geomembrane is greater in the dam crest and but aslo that is even greater at the anchorage zone, the stress and strain at the anchor end of foot slope reach the maximum.The result has certain positive significance for the design of actual project.