As an emerging method for mildly molding polymer hydrogel bioscaffolds, the enzymatically polymerized system is mainly based on the screening of various oxidoreductases to produce radicals, but the design of multifunctional nanoinitiators to facilitate hydrogel performance remains challenging. Here, we utilize N-hydroxyimide-modified silica nanoparticles as nanoinitiators to simultaneously trigger glucose oxidase anaerobic polymerization and nanoparticle-grafting enhancement of the gelatin-polyacrylamide (PAAM) hydrogel. The enzyme-nanoinitiator system produced nitrogen radicals, which were further converted into carbon radicals via GOx-catalyzed glucose reduction, as confirmed by electron paramagnetic resonance (EPR) analysis. Our stretchable hydrogel has a 12-fold increased fracture energy relative to traditional hydrogel due to grafting enhancement by the nanoinitiator. The temperature-dependent physical crosslinking of gelatin endowed our hydrogel facile printing ability. Cytotoxicity assay and 3D cell culture demonstrated the low toxicity of our hydrogel. As the first example of the use of nanoinitiators for enzymatic polymerization, this work provides a biocompatible platform to prepare or print hydrogel bioscaffolds with the required mechanical strength.