Sheet beam is a kind of electron beam， whose cross-section is approximate rectangular or elliptical shape with high aspect ratio. Compared with conventional pencil beam， sheet beam has many advantages， such as high beam current and large interaction area. Terahertz science and technology have got rapid development in recent years owing to its high frequency， wide bandwidth， high-speed transmission rate， and other advantages of terahertz waves. As a kind of new-type vacuum electron devices， terahertz sheet beam devices have excellent performance such as high power， high gain， high efficiency， and miniaturization. However， it is difficult for sheet beam to keep stable transport over a long distance due to the existence of Diocotron instability， which cannot lead to fully demonstrating its technical advantages. This paper briefly summarizes the generation， formation， and focusing methods of sheet beam， and then introduces the state-of-the-art of terahertz sheet beam devices. Finally， the challenges and development tendencies are discussed.