The contrastive corrosion experiments between surface nanocrystallined Zircaloy-4 and coarse-grained Zircaloy-4 under the condition of 673 K/10.3 MPa in pure water are carried out, and the microstructure of oxide films has been studied. The results indicate that the growth rate of oxide films formed on the nanocrystalline Zircaloy-4 is lower than that of oxide films formed on the coarse-grained Zircaloy-4. Simultaneously, the oxide/metal interface of the former is more regular and glossy than that of the latter. For nanocrystalline Zircaloy-4, the low oxygen diffusion rate through the oxide/metal interface can hinder the reaction of oxygen ion with metal ion. Furthermore, more tetragonal ZrO2 are observed in the oxide films, which can delay the martensite phase transition from tetragonal to monoclinic phase in oxide films. The contrastive corrosion experiments between surface nanocrystallized Zircaloy-4 and coarse-grained Zircaloy-4 under the conditions of 673 K / 10.3 MPa in pure water are carried out, and the microstructure of oxide films has been studied. The results indicate that the growth rate of oxide films formed on the nanocrystalline Zircaloy-4 is lower than that of oxide films formed on the coarse-grained Zircaloy-4. Simultaneously, the oxide / metal interface of the former is more regular and glossy than that of the latter. For nanocrystalline Zircaloy-4, the low oxygen diffusion rate through the oxide / metal interface can hinder the reaction of oxygen ion with metal ion. Further tetragonal ZrO2 are observed in the oxide films, which can delay the martensite phase transition from tetragonal to monoclinic phase in oxide films.