In hydrogen energy and thermal fusion energy, hydrogen isotopes permeation barriers (HIPB) are used to reduce hydrogen isotopes permeation, which may result in hydrogen isotopes leak and construction materials brittleness. Here, we made Er2O3 HIPB by magnetron sputtering and studied the relation between deuterium-permeation reduction factor (D-PRF) and coating thickness, micro-morphology. The 0.2 mu m Er2O3 coatings can reduce deuterium permeation by 1/10 similar to 1/20 at 600 degrees C similar to 300 degrees C. However, the reduction ability decreases gradually with the increase in coating thickness when the coatings are thicker than 0.2 mu m. The reason may be ascribed to the deuterium invasion in deuterium permeation test. After deuterium invasion into coatings, the coatings suffer intrinsic stress, thermal stress and expansion stress from deuterium invasion. As a result of grain size dependence on coating thickness in PVD-derived coatings, i.e. grains become coarse with increasing coating thickness, the sum of stresses in various type increases with increasing coating thickness. The coatings crack easily when they suffer more strong tensile stress. So, the damages of coatings become serious and D-PRF reduces with increasing coating thickness. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.