Jiu Duan Line refers to a U-shaped discontinuous line marked on the map of South China Sea in China, which is also called U-shaped line, South China Sea discontinuous line, island ownership line, traditional coastline, discontinuous national boundary line, historical right line and historical waterline by some experts and scholars. In the South China Sea, China uses the Nine-Segment Line of the South China Sea to represent the traditional territorial scope, and exercises sovereignty, jurisdiction and historical rights within this line.