Abstract: The surface chemical behavior of clean uranium metal in hydrogen atmosphere at 100 and 200 ℃ is studied by X ray photoelectron spectroscopy (XPS), respectively. It leads to hydriding reaction when the hydrogen exposure is 12.0 Pa·s, and the U 4 f 7/2 binding energy of UH 3 is found to be 378.7 eV. The higher temperature (200 ℃) is beneficial to UH 3 formation at the same hydrogen exposures. XPS elemental depth profiles indicate that the distribution of uranium surface layer is UO 2, UH 3 and U after exposure to 174.2 Pa·s hydrogen.