In the differential optical absorption spectroscopy (DOAS) measurement, the accuracy of the pollutant concentration is determined by the selected spectral resolution. The effect of spectra resolution on the detected characteristic absorption structure of gaseous pollutants and the variation of differential cross section of gaseous pollutants with the change of resolution are studied. The effect of spectra resolution on the detection limits of gaseous pollutants is deduced, and the functional dependence of the signal-to-noise ratio (S/N) on the spectral resolution is reduced by studying the relationship between light intensity and spectral resolution, from which the resolution is determined for all the gaseous pollutants with the optimal S/N. The measurement error in detecting the standard gases at different spectral resolution is calculated. The optimized resolution range are determined for the gaseous pollutants, which can yield high sensitivity, good selectivity and reasonable time resolution for the accurate qualitative and quantitative analysis of NO2, O3 and SO2. The real time monitoring of NO2, O3 and SO2 are carried out in the Fengtai district of Beijing, and the measurement result is in good agreement with the result of point instruments.