Abstract: In order to quantitatively analyze the reliability of geomembrane surface barrier on rockfill dam, a stochastic method based on the principle of the maximum entropy is employed to analyze the random contact between geomembrane and particle underlayer. The distribution of contact force between geomembrane and particle underlayers with different particle sizes and sharpnesses under different pressures can be obtained theoretically using this method. Two simple cases are also given to show the detailed process of mathematical derivation of this method. The distribution of contact force is exponential according to the proposed method, and the particle size and pressure are the most two important factors to affect the distribution of contact force. The proposed method is then verified by a series of laboratory experiments using the pressure-sensitive film, and it is a reliable tool to measure the contact force at each contact point. The results show that the distribution of contact force from the proposed method is in good agreement with the test data.