Abstract: In this paper the evolution characteristics of the microstructure of the oxide film of nanocrystalline zircaloy-4 have been studied with x-ray diffraction （XRD） technology. The oxide film is formed in water corrosion circumstance at 400℃. The results show that the evolution of the oxide film structure of nano-crystalline zircaloy-4 is similar to that of the normal zircaloy-4 with coarse grain size. However, the preferred orientation in nano-crystalline zircaloy-4 is found at low exponential plane, such as （101） and （102）. The grain size of the oxidation film of nano-crytalline ZrO₂ is smaller than that of the normal crystalline plane. The experimental results also show that the transformation speed rate from tetragonal phase （t-ZrO₂） to monoclinic phase （m-ZrO₂） in the oxide film of nano-crystalline zircaloy-4 is less than that in the oxide film of normal zircaloy-4 with coarse grain size. Thus, the nano-crystallized treatment can result in the changes of the corrosion dynamics process of the zircaloy-4 alloy. And these changes have been discussed in the paper.