In order to find out whether the loading medium has an effect on the mechanical properties of the expansion deformation of the geomembrane, the HDPE geomembrane with three thicknesses of 0.2mm, 0.3mm and 0.6mm were selected as the research object, and the air and water were used as the loading medium respectively. The spherical bulging deformation test under the ring constraint was carried out, and the following conclusions were drawn : (1) The loading medium has a great influence on the bursting pressure and bulging height of the geomembrane during the expansion of the geomembrane. The bursting pressure under the water expansion is about