Abstract: With the rapid development of Internet technology, especially flexible electronics, stretchable electronic materials have shown broad application prospects in flexible electronic products and wearable devices. In this study, a high‑performance composite hydrogel was prepared by incorporating a mixture of hexagonal boron nitride (h‑BN) and gallium‑based liquid metal (GaInSn) into a polyvinyl alcohol (PVA) matrix. The resulting hydrogel exhibits excellent mechanical properties and electrical response. It shows a high tensile strength (3.01 MPa), an ultralarge elongation at break (up to 847%), and a stable, continuous resistance change with strain, as well as good fatigue resistance under cyclic tension. Flexible strain sensors fabricated from this composite hydrogel can sensitively capture human joint motions and produce clear and highly repeatable electrical signals. The synergy of h-BN and GaInSn provides a new material design strategy for the development of high-performance flexible wearable strain sensors.