The crystal structure of the oxide film of NZ8 alloy, corroded by static autoclave test in 360 °C Li water and 400 °C steam was investigated by Raman spectroscopy method in this paper. The results indicate that the oxide film of NZ8 alloy is mainly composed of monoclinic ZrO2, including a small amount of distorted tetragonal ZrO2. With the prolongation of corrosion time, the average content of the distorted tetragonal ZrO2 in the oxide film decreases, that of monoclinic ZrO2 increases, and tetragonal ZrO2 transforms into monoclinic ZrO2. From the oxide/metal interface to the surface of the oxide film, the content of tetragonal ZrO2 reduces gradually and it is the highest at the interface. At the same time, the tetragonal ZrO2 content at the interface of NZ8 alloy oxide film , gained in 360 °C Li water for 98 d, is much higher than that in 400 °C steam for 70 d, and tetragonal ZrO2 is not observed at the surface of the oxide film exposed to 400 °C steam. The transformation from tetragonal ZrO2 to monoclinic ZrO2 decides the corrosion properties of NZ8 alloy. Corrosion resistance is improved when the content of tetragonal ZrO2 in oxide film increases.