Zinc–air batteries (ZABs) with high energy density and low cost have ignited tremendous interest in meeting the ever-growing demands for flexible and portable electronics. As the “blood” of a flexible ZAB, the semi-solid/solid-state electrolyte plays a critical role in the battery performance such as cycling performance, rate characteristics and power output. Herein, a novel porous-structured poly (vinyl alcohol) (PVA)-based nanocomposite gel polymer electrolyte (GPE) with the optimum addition of silica (SiO2) was synthesized and utilized in a bendable sandwich-type ZAB. The fabricated porous PVA-based nanocomposite GPE exhibited a high ionic conductivity (57.3 mS cm–1), excellent water retention capability as well as improved thermal and mechanical properties under ambient condition, with which the assembled flexible ZAB presented excellent cycle stability, discharge performance and power density. Furthermore, the flexible porous PVA–SiO2 based ZAB sets could power a light-emitting diode screen, a handheld electric fan, or even a mobile phone, demonstrating its promising potential for high-performance ZABs with high safety, cost-effectiveness, and excellent flexibility.