In this paper, a novel technique combined light-electronic microscopy and computer imaging trace was used to investigate the synthesis of thioether, which is an intermediate for lansoprazole. The reaction kinetics study by a visualization technique was carried out in a minireactor, and the concentration-grayscale standard curves for thioether were obtained by analyzing the grayscales of digital images for the solutions with 20 different concentrations. Based on the concentration-grayscale standard curves, the reactant concentrations at different times were calculated and the reaction kinetic curve as well as the reaction rate equation were obtained. It was found that the total mass-transfer resistance of sodium imidazole was larger than that of bromopyridine. Liquid-liquid interface of synthesizing thioether was observed and its mass transfer mechanism was discussed.