In order to understand further the gas-liquid two-phase mass transfer process mechanism in microchannel, by using the relationship between stripes and fluid refractive index and that between refractive index and the fluid concentration, the microscopic laser holographic interferometry is used to study the concentration distributions on the liquid side during the formation of Taylor bubble at the inlet of microchannel. The dimension of microchannel is 100 μm in depth, 2000 μm in width, and 4 cm in length. CO2 is used as gas phase and ethanol is used as liquid phase. The shift of the interference stripes during the absorption is recorded by image acquisition system, and the images are treated by a self-designed digital image processing system. Experimental results show that there is obvious mass transfer during the generation processes of Taylor bubbles, and both the liquid side concentration near the interface and the thickness of concentration boundary layer decrease with the increment of liquid and gas velocities. The results show that, for real-time determination of gas-liquid mass transfer process, microscopic laser holographic interferometry testing system can obtain clear images and satisfactory results in the micro scale channels.