Wavelength band selection method for target detection which is out of the atmosphere based on character of atmosphere radiation is proposed in the paper. In order to improve the target identification performance, wavelength band is selected by considering the target radiance, the background radiance, the target background contrast, the transmittance of slanting path and the response character of the sensor. By adopting atmospheric condition of the midlatitude summer model in the daytime, no clouds urban aerosols, spring-summer aerosol profiles and background stratospheric profiles extinct model, the typical spectrum characters of target background radiance, contrast and transmittance are computed by the radiative transfer computation software MODTRAN, and then the spectrum characters in the wavelength bands are analyzed. From the analysis results and the validation in other atmosphere models, the optimal detection wavelength band is selected.