According to the conversion of sRGB(Standard RGB) color space and CIE(Commission Internationale de L′Eclairage) colorimetric system and the character of the CIE 1931 chromaticity diagram,the MATLAB program was composed to achieve the conversion from the RGB information to the dominant wavelength or the complementary wavelength of one color,and then was utilized to analyze the images of the chromogenic products under the area light source.The quantitative detection of the pH value was realized with the color’s dominant wavelength and the detection of the nitrite with the color’s complementary wavelength.There are linear relationships between pH value and the color’s dominant wavelength of its chromogenic products in the pH value ranges of 4.0-7.0 and 7.5-10.0,respectively.And there is a favorable linear relationship between concentration(10-40 mg/L) of nitrite and color’s complementary wavelength of its chromogenic products.Combined with the Green value of the color,the range of detection by the traditional absorption spectrometry was enlarged.