Abstract: The space-based missile early warning system has different detection effect in different bands, and it is very necessary to select the appropriate detection band. In this paper, 11 kinds of missile plume spectra were studied and analyzed in the 2-5 m. Many influential factors were considered, such as the plume height from the ground, the atmosphere and cloud radiation, atmosphere attenuation, etc.. Principle of selection is relatively stronger radiation of target, distance of target-to-earth from high to low, wave bands from more to less. The number of bands can be controlled by setting the threshold. Finally, the paper selected bands at the center wavelength of 2.99, 3.06, 3.12, 4.6, 4.62 m. According to matching rules to fit out image that contains the characteristics of the target spectral, and signal-to-noise ratio(SNR) was analyzed for characteristic spectral image and full wavelength image. The results show that when the target reaches a certain height, SNR of characteristic spectral image is higher than that of the whole wavelength image.