Emulsion is a disperse system with two immiscible liquids,which demonstrates wide applications in diverse industries.Emulsification technology has advanced well with the development of microfluidic process.Compared to conventional methods,the microfluidics-based process can produce controllable droplet size and distribution.The droplet formation or breakup is the result of combined effects resulting from interfacial tension,viscous,and inertial forces as well as the forces generated due to hydrodynamic pressure and extal stimuli.In the current study,typical microfluidic systems,including microchannel array,T-shape,flow-focusing,coflowing,and membrane systems,are reviewed and the corresponding mechanisms,flow regimes,and main parameters are compared and summarized.