Abstract: The surface reactions of different oxide layers on uranium with CO at 25℃ and H₂ at 200℃ have been studied by X-ray photoelectron spectroscopy (XPS) respectively. After CO and H₂ adsorption on the surface oxide layer, the content of oxygen in the surface oxide is decreased and O/U ratio decreases with increasing the exposure of gases to the surface layer. The effect of reduction on metal surface is more obviously with increasing of oxide layer thickness. But the influence of H₂ is less than CO.It may lead to the hydriding reaction of uranium in hydrogen atmosphere at 200℃ when the oxide layer thickness is decreased and uranium oxidation state is lower.