Abstract: A spectrum measurement system was built by taking solar as light source. High precision imaging spectrometer was used to collect solar spectrum. A solar spectrum at a specific time was chosen as reference data to inverse concentration of NO2 at another time by combining the concentration of polluted air at that time and applying differential absorption theory. A new method of processing spectrum data was presented. It focuses on the application of origin 7.5 to spectrum analysis as well as the application of drawing the absorption cross section graphs according to HITRAN data base. The above-mentioned data may be used in the quantitative analysis of spectra lines with less error. The process of inversion features high accuracy of spectrum data and inversion parameter, which improves the accuracy of inversion concentration for NO2. The experimental results agree with those of other measurement equipment, which proves the inversion process is feasible.