Flexible strain sensors have garnered significant attention for their potential applications in advanced flexible electronics and wearable technologies. However, achieving stable signal transmission at high temperatures remains a major challenge. In this study, we developed a novel polyimide (PI) aerogel composite, reinforced with intrinsically short-cut polyimide nanofibers (PINF) that are surface-coated with silver nanoparticles to enhance both conductivity and mechanical strength. Carbon nanotubes (CNTs) are used as the main filler in synergistic effect with Ag@PINF particles to further improve the conductivity and sensing performance of the composite material. This synergistic design results in a flexible PI aerogel composite material with rapid response time (116 ms), high sensitivity (GF = 3.12), and long-term cycling stability (> 1000 cycles). Additionally, the sensing materials were tested at high temperatures and after high-temperature aging, demonstrating good flexible sensing performance. Experimental results demonstrate that the composite sensor maintains stable strain-sensing performance across a range of environmental temperatures, showing consistent strain response under the same deformation conditions. This work provides a promising approach for fabricating high-performance, temperature-resistant flexible strain sensors, with broad applications in flexible electronics and wearable technologies.