The general expression about signal-to-noise ratio ( SNR ) in spatial domain and spectral domain of spatial heterodyne spectrometer is deduced considering the primary noise, and the relationship between SNR and instrumental characteristic parameter is analyzed, which includes spectral resolution, spatial resolution, degree of interferogram modulation, electronics noise and so on. Combined instrumental characteristic parameter with imaging methods mode, the corresponding conclusion is obtained , and the results show that SNR can efficiently evaluate and reflect the character of spectrometer.