Method of solar occultation flux infrared spectroscopy to detect the pollution emission flux of sources is presented in detail. It is developed based on the FTIR technique. A Two-layer radiative transfer model is established theoretically. Algorithm of transmissivity calculation of pollution gas is expatiated. The method to obtain the absorption coefficient of molecules from HITRAN, NIST and QAsoft databases is mentioned. Levenberg-Marquardt algorithm is used to calculate column concentration of pollution gas from pollution source. The distribution of column concentration is drawn by software developed by our group. The total system and the sun tracker are shown in the paper. The distribution of column concentration of NH3 is measured in a chemical plant in Hefei China. The calculated distribution of column concentration of NH3 is consistent with the measured one in the chemical plant.