Using two different types of ionomers which are comprised of Nafion and hydrocarbon, we constructed systems of the ionomers on Pt catalyst surface, and investigated water content dependence on oxygen permeability in the ionomers using molecular dynamics simulations. We have found that the oxygen permeability of the Nafion-based ionomer is better than that of the hydrocarbon-based ionomer. Furthermore, the number of permeated oxygen molecules decreases with increasing water content on the both ionomers. Moreover, we analyzed density distributions of the ionomer components and solubility distributions of oxygen in the ionomers. As the results, in the ionomer-gas interface and bulk region of the both ionomers, the solvent molecules which increase as water content increases, block the oxygen permeation. In the ionomer-Pt interface of Nafion-based ionomer, the solvent occupies the pathways for oxygen permeation, while in the interface of hydrocarbon-based ionomer, the solvent which are piled up on the surface of high-density polymers, blocks the oxygen permeation.