The early fire warning of a wind turbine is very important to ensure its safe operation and maintenance. We developed a thermal hazard sensing device based on thermally released nanoparticles, by which the early fire of wind turbine electrical equipment can be found promptly. We first introduce commonly used methods for very early fire warning in power systems, analyze the thermal pyrolysis process of cables, and propose a detection approach for identifying thermal hazards by monitoring characteristic nanoparticles released during the thermal pyrolysis of hazardous materials. For detecting the nanoparticles emitted during the thermal pyrolysis of hazardous materials in wind turbines, experimental platforms were established. Combustion experiments were conducted on representative fire-prone materials generally used in wind turbines. From the results of these experiments, the characteristic nanoparticles associated with thermal hazards in wind turbines and their detection alarm thresholds were determined. On the basis of these findings, the device was developed and subjected to detection performance tests and anti-interference tests against water mist and dust. The developed device is currently applied in early fire warning systems for wind turbines, demonstrating its effective performance.