Abstract: Taking the natural clay in an enterprise in Changsha as the main raw materials, using the experiment method of water solution polymerization at the room temperature, a new type of sealing material was prepared by mixing bentonite and clay modified with polyacrylamide (PAM), which was used to seal the bottom area of flexible vertical impervious wall construction projects to prevent the groundwater from flowing around the bottom of the high-density polyethylene (HDPE) geomembrane. The influence of three different modifiers and the amount of bentonite on the permeability coefficient of the sealing material and the blocking and adsorption of hexavalent chromium were studied by laboratory experiments. The results showed that the permeability coefficient of the sealing material could be reduced when the bentonite was modified with PAM, while, to a certain extent, the hydroxypropyl methyl fiber and polyvinyl alcohol increased the permeability coefficient of the sealing material. With the increase of the amount of modified bentonite added, the permeability coefficient of the sealing material decreased gradually. In the simulated column migration experiment, the retention effect of the sealing material on pollutants could reach 68.5%. Based on a flexible vertical impermeability wall project in Changsha, no tracer was detected in the downstream receiving well in the tracer dispersion and migration experiment on the area of the built impermeability wall, indicating that the sealing material could effectively prevent groundwater from flowing around the bottom on the engineering application.