The calibration results of the transmissometers cannot be traced to the definition of meteorological optical range (MOR) of the World Meteorological Organization. How to realize the spectrum simulation of the 2700 K incandescent lamp in the MOR definition has become a key issue that needs to be solved urgently in the calibration technology of the transmissometers, so the spectral simulation method of calibration light source of the transmissometers is studied. First, the influence of spectral mismatch on the calibration of the transmissometers is analyzed theoretically, and the basis for discriminating the spectral distribution of the light source that meets the calibration accuracy requirements of the transmissometers is established. It is concluded that the spectral simulation errors of the calibration light sources of the transmissometers should be better than ±5.5%. Then, based on a transmissometer calibration light source system with digital micromirror device (DMD), and on the basis of genetic algorithm, a spectral simulation method based on a uniform division mechanism without residues is proposed. On the premise of dividing uniformly the array surface of DMD micro mirrors into 800 columns, the number of fitting units is increased by uniformly dividing the DMD array surface, and and the spectral simulation of absolute color temperature of 2700 K is realized. Finally, the spectral distribution of the calibration light source corresponding to 20, 50, and 80 basic spectral fitting units is tested, and the uncertainty is analyzed. The test result show that the spectral simulation error of the calibration light source corresponding to the 80 basic spectral fitting units is ±5.3%, and the expanded uncertainty is 4.04%.