The Signal to Noise Ratio(SNR）of thermal infrared hyperspectral system is greatly influenced by stray light which emits from optical system and signal decrease after being diffract.Cooling of the entire optical system can highly reduce system stray light,nevertheless the impact of dark current become obvious at low temperature.Theoretical analyzed signal component of thermal infrared hyperspectral system,divided camera output signal into four parts and measured each part of the signal so as to get percentage variation of each part of signal and trend of Noise Equivalent Temperature Difference(NETD）at normal and low temperature.Furthermore,critical factors influenced system performance are founded and scheme for improving system SNR was presented.These work would be the reference for the development and practicality of Chinese thermal infrared hyperspectral system.