Abstract: The common cushion layer used in the geomembrane face rockfill dam is made of granular materials such as gravel and non-fine concrete where bulge deformation or failure of geomembrane is very likely to occur in its surface holes. The curve intersection method based on the thin film theory is the common method used to analyze the bulge deformation of the geomembrane in the surface holes of cushion layer. However, it is inaccurate due to the neglection of horizontal (tangential) displacement of the geomembrane. Based on the FEM theory, a new method is proposed, which takes the horizontal (tangential) displacement of geomembrane into consideration, and is validated by the bulge tests on the geomembrane in a circular hole. The deformations and strains of the geomembrane in different shapes of holes are analyzed by this method, and different strain distributions and failure modes are obtained. The curve intersection method is also used to compare with the new method under the same condition. It is indicated that there is less difference in the deformation and average strain of the geomembrane when the water pressure is low. However, when the water pressure is relatively high, the influences of horizontal (tangential) displacement of the geomembrane on its strain should not be neglected.