Abstract: The period of validity of hohlraum in atmosphere is an important parameter, and the measurement for it is a crucial step in the R&D of hohlraum. By the surface analysis, the evolvement of O in the DU/Au foils in atmosphere was researched, and the crystal state of this foil was analyzed through XRD. It’s proved that the period of validity of this foil (O atomic percentage <5%) is between 18 d and 21 d, the crystal oxide isn’t discovered, and the crystal state of this foil doesn’t obviously change.