The corrosion behavior of zirconium alloy was investigated using synchrotron scanning transmission X-ray microscopy and X-ray absorption spectroscopy. Scanning transmission X-ray micrographs showed different electronic structures at the oxide/metal interface of Zr–Nb–Sn alloy after exposure to high-temperature hydrogenated water. The orbital hybridization structure at the oxide/metal interface exhibited weaker t2g and eg peaks in X-ray absorption spectra, suggesting that zirconium suboxide can form just above the oxide/metal interface. The suboxide layer that formed at a high dissolved hydrogen concentration is thicker than the suboxide layer that formed at a normal dissolved hydrogen concentration after 100 d of oxidation.