Previous studies have shown that the thermal infrared radiation of rock surface changes corresponding to the stress in the rock loading process. The effective extraction of radiation variation information depends on the influence from background radiation. Thus, this study aims to analyze the variety of thermal infrared spectrum for loaded rock under different experimental conditions. The thermal infrared radiation experiments of loaded granite were carried out in both indoor and outdoor conditions. The relationship between radiation variation and stress under different experimental condition was investigated, and the characteristic of radiation information caused by stress was analyzed. Furthermore, we compared the sensitive waveband to stress in thermal infrared detection under indoor and outdoor conditions. The results showed that the radiation background had a significant effect on the radiation changes of loaded rock. It was found that the infrared radiation changed more significantly, and correlated more closely to stress in the outdoor condition, while the sensitive waveband is wider due to the relatively weak background radiation. It is more accurately and reasonably for detecting the thermal infrared radiation of loading rock in the outdoor condition. The 8.0～11.8 μm wave range can be considered as the effective waveband for granite stress monitoring using thermal infrared remote sensing technology.