Electrowetting refers to the phenomenon of modifying the surface tension between a liquid and a solid by adjusting the externally applied electric potential between the liquid and solid electrodes, thereby changing the contact angle between the two and causing a deformation and displacement of the droplets. Electrowetting electronic paper display is a new reflective “paper-like” display technology based on a rapid response microfluidic control technology. It has the advantages of low energy consumption, visual health, and flexibility of commercial electrophoretic electronic paper display products, while breaking through the bottlenecks of “full-color” and “video-speed response” that currently restrict the application of electronic paper display technology. In this paper, several physical directions involved in electrowetting display devices, especially wetting and electrowetting, binary phase fluid mechanics, microscopic and interfacial physics, photophysics, dielectric physics, thermophysics, and transient physics, are systematically reviewed; the basic principles of device operation, microscopic and mesoscopic physical pictures, internal mechanisms of device operation, and device reliability are also discussed in detail.