Abstract: To verify the feasibility of geosynthetic clay liners(GCL) as liners material for coal gangue impoundment, diffusion tests were conducted with vertical double reservoir method to determine the diffusion ability of heavy metals(Zn²⁺、Mn²⁺) and sulfate from coal gangue leachate in GCL-S(Sodium-activated bentonite), and POLLUTE V7 based on finite layer method was used to draw the fitting curve of pollutant changing with time in the diffusion device, which calculated the diffusion coefficient of contaminants in GCL. The data show that the diffusion coefficient in GCL was lower than that in compacted clay liners, so GCL could control the diffusion and migration of pollutants more effectively.