Abstract: In view of the problem of bending (folding) of anti-seepage geomembrane in the design and construction of the anti-seepage structure of membrane-faced rockfill dam, the bending nature is divided into two types: structural bending and non-structural bending. In order to quantitatively evaluate the damage caused by the bending and its laws, the parameters affecting the bending deformation of geomembrane are deduced based on the thin plate (shell) theory of stability theory, and a set of test equipment is independently developed on the basis of theoretical analysis. Two different PVC geomembranes are selected as the experimental materials, and under the maximum bending angle of 90 degrees, the 4℃ water temperature test environment is simulated. The test results show that the bending effect causes the attenuation of mechanics performance index of the geomembrane. After the bending effect of 120 days, the attenuation degree of fracture strength of SY-GM type geomembrane reaches 58.71%. Based on the analysis results of experimental data, some measures are proposed to reduce the attenuation degree of the index by increasing the bending radius of curvature and reducing the bending angle of curved surface.