Under certain conditions, the relevant index components in food samples can react specifically with the chromogenic agent to generate products with different shades of color, which can selectively absorb visible light with different wavelengths. Color depth, that is, absorbance, is related to the concentration of index components in the sample, and obeys Lambert-Beer law in a proper concentration range. Therefore, the detected absorbance value can be automatically calculated by the standard curve software built in the instrument, and the accurate concentration of the index components in the sample and whether it exceeds the standard can be obtained.