The poison of Pd membrane in CO2 at different temperatures and the hydrogenization of the poisoned membrane were carried out in a silica tubular furnace and the hydrogen isotope permeation capacity was tested. The variation of Pd membrane phase and morphology was analyzed and observed by XPS and SEM. The cause and the mechanism of the variation were discussed. The results show that the molecule CO2 will dissociate to C=O, C–O and O on Pd membrane surface. The adsorptive capacity of C–O and O increases and that of C=O decreases with increasing of the temperature. PdO and micropores can be detected apparently when the poison temperature reaches 500 oC, and C–O will be adsorbed on Pd membrane surface firmly. After hydrogenization, the PdO, C–O and free O on the Pd surface vanish while C=O reappear. After the Pd membrane is poisoned by CO2, the hydrogen isotope permeation capacity of Pd membrane decreases because the atom O and C–O occupy H site and react with atom H easily