To realize high performance flexible transparent electronics with extreme environmental adaptivity, Ag nanowires (Ag NWs) electrodes should simultaneously meet the requirements of high-temperature tolerance, chemical and mechanical robustness. Herein, a scalable Ag NWs bundle micro-meshes embedded in polyimide (Ag BMs/ePI) conducting film via a facile spray coating and transfer method is reported. Due to the synergistic effect of bundle micromesh and embedded architecture, the Ag BMs/ePI electrode exhibits high thermal stability (370 °C and 400 °C under ambient and nitrogen atmosphere conditions, respectively), low sheet resistance variation (<4%), good corrosion and deformation resistance. As an electrical heater, the Ag BMs/ePI can achieve ~204 °C with the fast thermal response time of ~8 s at 8 V, and exhibits good heating stability under bent condition. This work offers a promising platform for the emerging flexible transparent electronics to adapt extreme environments, especially for those devices which require high-temperature processing.