In order to understand the moisture diffusion, we combine the obstruction-scaling model with the moisture clustering in confined spaces of the polymer hydrogel, with relevance to the performance of the super desiccant polymer. Special attention is focused on elucidating the effect of chain stiffness by considering the conformation of polymer chain on the basis of polymer physics. Relevant parameters for calculations are determined from literature information as well as the best fits for reported data performed with the copolymer. Our results exhibit the moisture diffusion decreases with increasing chain stiffness represented by the persistence length. Note that the larger persistence length provides smaller radius of openings in void spaces, resulting in the stronger hindrance effect on the moisture diffusion. Higher temperature makes the water molecules to be easier to form clusters, which provides the decrease in diffusivity. The increase of moisture diffusion at low humidity is attributed to the swelling of the chain, whereas its decrease at high humidity results from the water clustering.