Microflow reaction is important for the miniaturization of chemical devices and systems. From an engineering perspective, excellent characteristics, including narrow residence time distribution, rapid reactant mixing, fast mass and heat transfer, and effective droplet morphology control, of segmented liquid–liquid flow in microspace are summarized in this review based on recent research progress in the areas of microfluidics, flow chemistry, micro total analysis, and microreaction engineering. Via engineering, important roles of segmented liquid–liquid flow, such as improvements in production yield, inline purification of intermediates and products, creative droplet reactors, and preparation of particle materials with various structures, are introduced. The scale-up of micro devices and large-scale production of chemicals through microflow technology are also discussed, showing good prospects in research and industrial application.