First-principles plane wave calculations based on spin-polarized density functional theory (DFT) and generalized gradient approximation (GGA) have been used to study the adsorption of H atoms on cubic Er2O3 (001) surface. We identify stable adsorption positions and find that H preferentially adsorbs on top of fourfold-hollow sites and transfers electrons to the surface, resulting in the formations of covalent bonds to the nearest neighboring four oxygen atoms. In the most energetically favorable adsorption sites, It was found that H bonds with O atoms at the cubic Er2O3 (001) surface with an adsorption energy of −295.68kJmol−1 at coverage 1/8ML, and the adsorption energy is inclined to decrease with the increase of H coverage (>1/4ML). In addition, our calculations indicate that the dissociative H atom configurations have adsorption energies that are at least 152.64kJmol−1 greater than the H2 molecule configurations on the surface. These results discussed in the context of erbium oxide slabs are employed to rationalize some processes regarding to the hydrogen isotope permeation behavior of tritium permeation barrier.