According to the Noxon method,the absorption characteristic of NO2 in the wavelength region 430-450nm is used to measure the NO2 Vertical Column Density (VCD) in the urban area .A new optical method using the differen tial optical absorption spectroscopy is developed to measure the NO2 VCD in the urban areas by using the solar light as the source, C-MOS linear imag e sensor as the detector and the sun spectrum taken at the summit of Yellow Moun tain as the reference spectrum.