Abstract: The oxidation behavior on two kinds of nuclear grade stainless claddings in 350 ℃/22 MPa high temperature and high pressure water were carried out by SEM, XRD and XPS. The results show that, with increase of oxidation duration, the number and the size of oxide particles as well as the thickness of the oxide film increase slowly. The oxide film formed on the surface of the stainless steel cladding materials exhibits bi-layer structure with Fe-rich outer layer and Cr-rich inner layer, and contains Fe-Cr oxides mainly. The number of the oxide particles and the thickness of the oxide film decrease with increase of Cr content, while post-weld heat treatment (PWHT) contributes to the increase of the number of the oxide particles and the thickness of the oxide film.