To investigate the diffusion behaviors of Cs(I) and Eu(III) on a novel copper-modified montmorillonite material (Cu-montmorillonite), experimental investigations were conducted using the capillary method. The experimental results showed that the diffusion decreases with increasing the compaction density and ionic strength. The experimental study further employed Archie's law and the Glaus' model to quantitatively assess the impacts of porosity and ion concentration on diffusion. This work can provide potential applications in deep geological nuclear waste repositories.