This study aims to visualize the mixing and chemical reactions of aqueous solutions in microchannels by using a near-infrared absorption imaging technique based on the spectral characteristics of water and solutes. This paper focuses on the effect of the salt generated from neutralization reaction of HCl and NaOH aqueous solutions on the spectra, and tries to construct the concentration images of the salt by using absorbance difference images at the wavelength of 1412 nm and 1442 nm.