Relatively high volumetric shrinkage induced by polymerization of photopolymer severely limits its applications in high-density holographic storage. In this paper, what we believe to be a novel organic-inorganic hybrid nanoparticles (NPs) of octaphenyl-polyhedral Oligomeric silsesquioxane (POSS) are employed into polyvinyl alcohol (PVA)/acrylamide photopolymer with 300µm thickness. By optimizing the concentration of octaphenyl-POSS, the volumetric shrinkage is successfully suppressed from 1.11% to 0.41%, and satisfies the requirements of commercial holographic data storage (HDS) material. Moreover, the introduction of POSS NPs does not sacrifice other holographic recording capacities. Contrarily, the diffraction efficiency of photopolymer after dispersing 2‰(w/v) POSS increases from 86% to 90%. The physical mechanism of enhanced capacities is discussed by using photopolymerization and NPs diffusion process. To our knowledge, this is the best results of PVA/acrylamide photopolymer with low volumetric shrinkage, high diffraction efficiency and angular selectivity. The POSS-dispersed photopolymer system is expected to have good application prospects in angular-multiplexing high-density 3-D holographic storage.