Abstract: Composite geomembrane is an ideal impermeable material because of its high mechanical strength and good anti-seepage property. Coupled equations of stress-strain and seepage are adopted in the paper to analyse and calculate the common action of stress, strain and seepage on the core dam in Zhushou reservoir in which composite geomembrane laid on upper stream sides of gravelly clay core wall was combined to prevent seepage. In view of the different property of soil at the two sides of composite geomembrane, the relative slide is considered, it can be treated according to contact element, and linear element in the calculation owing to that composite geomembrane which possesses high tensile strength can restrain the soil strain.