From the digital images of the red complex which resulted in the interaction of nitrite with N-(1-naphthyl) ethylenediamine dihydrochloride and P-Aminobenzene sulfonic acid, it could be seen that the solution colors obviously increased with increasing the concentration of nitrite ion. The JPEG format of the digital images was transformed into gray-scale format by origin7.0 software, and the gray values were measured with scion image software. It could be seen that the gray values of the digital image obviously increased with increasing the concentration of nitrite ion, too. Thus a novel digital imaging colorimetric (DIC) method to determine nitrogen oxides (NOx) contents in air was developed. Based on the red, green and blue (RGB) tricolor theory, the principle of the digital imaging colorimetric method and the influential factors on digital imaging were discussed. The present method was successfully applied to the determination of the daily changes curve of nitrogen oxides in the atmosphere and NO-2 in synthetic samples with the recovery of 97.3％-104.0％, and the relative standard deviation (RSD) was less than 5.0%. The results of the determination were consistent with those obtained by spectrophotometric method.