The poison of palladium membrane in H2O (gas) and the hydrogenization of the poisoned membrane were proceeded in a silica tubular furnace. The hydrogen isotope permeation capacity of palladium membrane was tested. The variation of palladium membrane phase was analyzed by XPS and SEM. The causes and the mechanism of the variation were discussed. The results show that the content of adsorptive C and O on the palladium surface can be decreased by the reaction between H2O (gas) and palladium surface without variation of chemical state. Some cracks can be observed on the palladium surface at a higher reaction temperature, which account for a physical change. At room temperature, there are no obvious changes on the palladium surface after the palladium membrane deoxidized again by H2. The deuterium permeability of Pd membrane which has reacted with H2O (gas) is higher than the original membrane. The improvement of deuterium permeability could be ascribed to the improving surface cleanness caused by the reaction between H2O (gas) and palladium surface.