Abstract: Based on the theory of blackbody radiation, the influencing factors in detecting spatial target with a hyperspectrometer were analyzed. The radiation from the sun to the surface of an object was calculated. The sky diffusion radiation from visible to near infrared was analyzed with MODTRAN software. The calculation method for the target and background radiant energy received by the imaging spectrometer is given. The general expression of SNR was deduced. The feasible means to get the high SNR is put forward by analyzing the effect of all the factors on SNR.