The problems of detailed X-ray characterization of pure nanostructured materials subjected to severe plastic deformation, namely large plastic deformation under applied high pressure without decomposition of a sample, are considered. Computer simulation has been used to interpret obtained experimental results. An analysis of applicability of various X-ray methods for determination of grain size in nanostructured materials has been carried out. Possible dislocation configurations responsible for specific defect structure formation due to severe plastic deformation have been determined.