Common infrared sources are similar to grey body radiation sources. Only little parts of radiation energies lie in the band of infrared atmospheric window, which affects their applications remarkably. Based on the analysis on band radiation power density and efficiency of infrared sources, the methods to enhance power density and efficiency by controlling spectrum emissivity of radiation source are proposed. The methods to control emissivity are analyzed. And the relative theories are applied to design a thin film of photon crystal to realize emissivity band choosing. The relative methods and results are useful to improve infrared sources and band efficiency.