As a main pollution gas, the emission of NO2 is endangering to the environment and human health, which should be monitored to achieve better governance. The existing imaging detection methods possess the advantages of a wide application range and good real-time performance, while accuracy and applicability are concerned in the reconstruction background. A method for quantitatively monitoring gas concentration using images of dual-channel target gas is proposed in this study. The NO2 concentration is retrieved from the ratio of 405 and 470 nm dual-channel light intensity, and the following theoretical and experimental research is carried out. Specifically, the relationship between gas column concentration and dual-channel light intensity ratio is obtained according to theoretical derivation. The effect of the dual-channel exposure time on the calibration equation is analyzed. The collected dual-channel light intensity ratio is compared with the theoretical value, and the difference between them is 0. 26% . The optimal value of dual-channel light intensity ratio under different solar zenith angles is measured by collecting the solar scattered radiation spectra at 26. 08° north latitude under various meteorological conditions. The performance of the detection camera is analyzed, and the detection range is 19. 6 ppm m. Concentration calibration and retrieval experiments give a calibration function, retrieve the two-dimensional distribution of gas concentration in diffusion, and validate the reliability of the dual-channel spectral imaging method for quantitative detection of gas concentration.