The emergence of biodegradable nanogenerators (BD-NGs) has provided a promising and safe approach for the development of biotransient medical electronics. However, the rapid advancement of these devices faces a major challenge due to the low output performance of BD-NGs. To address this issue, we develop a high-performance and fully biodegradable piezo-triboelectric hybrid nanogenerator (FB-HNG) for the first time. The FB-HNG is based on a sandwich-like heterostructured piezoelectric film composed of PVA/Gy/PVA. By utilizing an electric field-assisted water evaporation method to modulate the crystal process, a PVA/Gy/PVA film with enhanced piezoelectric properties (maximum d33 of 9 pC/N) is prepared. The surface of PVA layer is designed to rub against a PLGA film, forming the triboelectric part, while the inner Gy bulk layer provides impressive piezoelectric output. Through the coupled effects of triboelectric and piezoelectric mechanisms, a maximum output voltage and current of 94   V and 2.3 μA are achieved, respectively. Notably, the current density of 1.53 μA/cm2 and charge density of 6.53 nC/cm2 of the FB-HNG are the highest among reported BD-NGs. Furthermore, the FB-HNG also presents excellent biocompatibility and biodegradability both in vitro and in vivo, which highlights its potential and prospects as a power source for transient medical devices.