Structural changes during tensile stretching deformation for pure polypropylene (PP) specimen and PP/ZnO specimens with different content of ZnO nanoparticles have been investigated by small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) techniques. For pure PP specimen, there is a large amount of cavities appearing during stretching. The cavities are first extended in the equatorial direction and then elongated along stretching direction. At high strain some edge dislocations appear in PP lamellae structures. For PP/ZnO specimens, lamellar structures are destroyed gradually during stretching. At low ZnO loading (<0.5%), after stretching to strain of about 500%, the scattering intensity of cavities and dislocations is a little lower than that from pure PP. For the case of high ZnO loading (>0.5%), the scattering intensity of cavities and dislocations increases linearly with ZnO content. WAXS results indicate that, compared with the undeformed specimen, the crystallinity of all specimens shows a little decrease after stretching to about 500% strain.