The method of the characteristic matrix was used to analyze the suppression effect of photonic crystals on atmospheric window band emission. Several combinations of substrates and photonic crystals were considered, also discussed were photonic crystals construction and spontaneous radiation. It is found that, when the substrate is aluminum at 100°C, with photonic crystals consisting of Si (of high refractive index) and KCL (of low refractive index), the emissive power between 3∼5 μm of the combination surface is reduced to 0.101 W∕m², for comparison, the corresponding emissive power of aluminum surface is 0.302 W∕m². With photonic crystals,...