Nowadays, a lot of research have been done about the diffusion process, generally motivated by the diffusion process in oil and between liquids. In addition, improving the sensitivity and performance of laser beam deflection measurement system is an attractive subject in materials and instrumentation research. In this study, diffusion coefficient measurement system based on laser beam deflection has been developed to specify the diffusion coefficient of liquid-liquid material and well succeeded by following the Wiener experimental method. The Sodium chloride and water solution are poured into the diffusion cell and then illuminated by the laser beam that forms a line tilted 45° to the vertical. Image processing and measurement have been performed to specify the refractive index gradient and the diffusion coefficient. The diffusion coefficient of Sodium chloride is discovered to be in a good agreement with the literature.