Contrast-variation small-angle neutron scattering (CV-SANS) was applied to investigate the deformation mechanism of high-performance nanocomposite polymer hydrogels (NC gels) consisting of polymer chains and inorganic clay platelets. Anisotropic SANS functions were obtained at various stretching ratios, lambda 's up to lambda=9 and were decomposed to three partial structure factors, S(ij)(Q parallel,Q perpendicular). Here, the subscripts i and j denote the polymer (P) or clay (C) and Q parallel and Q perpendicular are the magnitude of the scattering vectors along and perpendicular to the stretching directions, respectively. SCC(Q parallel,Q perpendicular) and S_{PP}(Q parallel,Q perpendicular) suggested that the orientation of clay platelets saturated by lambda approximately 3 , while the polymer chain stretching continued by further stretching. On the other hand, SCP(Q parallel,Q perpendicular) , only available by CV-SANS, indicated the presence of a polymer-enriched layer adsorbed to clay surface, which are responsible for large extensibility of NC gels over 1000% strain and large toughness exceeding 780 kPa.