In this study, the PdAg membranes are prepared and applied for H2 separation and the effect of H2O(g) on their permeation properties have been studied. Two kinds of surface modifications, manual or suction-assisted methods are used to reduce the pore size of the Ag substrate and the PdAg membranes are then deposited on the modified substrates by different cycles of electroless plating (ELP) and electroplating (EP) processes. The samples prepared by ELP and EP processes on manual or suction-assisted methods can reach the gas tight level with the hydrogen flux of about 0.5 or 1.1 (mol-m− 2-s− 1) under pressure difference of 400 kPa. In terms of the H2O(g) effect on the H2 permeation, the hydrogen flux with H2O(g) are 0.3 and 1.0 (mol-m− 2-s− 1) for manual and suction modified samples, when applied pressure difference of 400 kPa and the depletion ratio is 40 and 9%, respectively, much smaller than those reported in the literature. The controlling process is mass transfer for both two samples, resulting from the competition effect of H2 and H2O(g).