The uniformity of the gas-liquid two-phase flow and slug bubble in a symmetrical parallelized branching microchannel were studied by using a high-speed camera system. The glycerol-water solution containing 0.3% SDS and nitrogen were used as the liquid phase and the gas phase respectively. Two flow patterns of slug flow and bubble flow were observed

and a flow pattern and a flow pattern transition line composed of two-phase operation conditions were made. The results show that the non-uniformity of bubbles is caused by the hydrodynamics interaction between the two channels

the hydrodynamics feedback of the downstream channels

and the manufacturing differences of microchannels. With the increase of viscosity of the liquid phase

the uniformity of the bubbles becomes better. The bubble size distribution can be more uniform for high liquid flow rates and low gas pressures. The prediction models of bubble size in both microchannels were established based on the conservation principle of pressure drop and the gas-liquid two-phase flow resistance model.