A nanocrystalline surface layer was fabricated on a pure zircaloy-4 plate by using the high-speed shot peening (HSSP) technique. The microstructural evolution of the zircaloy-4 was characterized by using X-ray diffraction, and transmission electron microscopy(TEM). After the high-speed shot peening treatment, obvious grain refinement was observed and a nanocrystalline surface layer was found. The grain size increased along with the distance far from nanocrystalline surface. The nanocrystallization mechanism was analyzed in terms of the deformation behavior and TEM observations of the microstructural evolution of the treated samples