The thermal infrared spectrum is a very useful band for earth-observation hyperspectral remote sensing. Due to the limitation of technology, the hyperspectral imaging system of thermal infrared spectrum in domestic space photoelectric system is not very common, but it has developed quickly and made great progressunder the support of national related department in recent years. Based on the airborne thermal infrared hyperspectral imager′ developing during the Twelfth Five-Year Plan period, the signal flow model of the system was established in this paper. The background radiation of the system was modelled and simulated, the dark current of the infrared focal plane component was analyzed and measured, and on this basis the factors affecting the detection sensitivity of the system were analyzed, the design rules of the cryogenic optical 100 K for the cryogenic temperature was presented. After the completion of the airborne thermal infrared hyperspectral imager, the comparison between the actual detection sensitivity and the simulation results was carried out. The results show that the system has good compliance and has accumulated important data for the further development of thermal infrared hyperspectral imaging technology.