A high-strength polyvinyl alcohol (PVA) hydrogel was prepared via a facile photocrosslinked polymerization with cellulose nanofibrils (CNF) reinforcement. The mechanism of CNF reinforcement was studied systematically. The hydroxyl groups in the surface of CNF generate hydrogen bonds with the pendant hydroxyl of PVA chains, which promotes the interaction of already chemical crosslinked PVA chains and increases the crystallinity of the resultant PVA-MA/CNF hydrogel. By optimizing the CNF incorporation content to the PVA-MA/CNF hydrogel, a compressive fracture stress of 490 kPa was obtained, which is higher than that of previously reported nanocellulose reinforced PVA hydrogels. And more importantly, this gel exhibits excellent cyclic compressive performance. This work provides a novel method to improve the mechanical strength of PVA hydrogel which is beneficial for its application in tissue engineering field.