Possessing certain spectral radiation characteristics in a relatively stable state, the air target can be identified according to its spectrum. At first, with the simulation model of air target spectral radiation, the spectral radiance was calculated. Secondly, successive projections algorithm was applied to extract the characteristic wavelengths from the simulation spectral data to reduce required data while retaining a certain accuracy. At last, the hybrid spectral similarity measure named SID (TAN) was involved in comparing the spectral radiation characteristics of different flying heights and flying time in 3-5 μm band and 8-14 μm band called dual atmospheric windows due to its stronger discrimination capability. The result shows that flying heights exert a greater effect on target spectral radiation characteristics than flying time. Meanwhile, changes in 3-5 μm band are more obvious than in 8-14 μm band. Therefore, aiming to improve the recognition accuracy, more factors are supposed to be considered in 3-5 μm band than in 8-14 μm. Compared with flying time, it is recommended to select more spectra of various flying heights as reference spectrum.