The Great Flood of Gun-Yu (Chinese: 鯀禹治水, romanized: Gǔn yǔ zhìshuǐ), also known as the Gun-Yu myth, was a major flood in ancient China that allegedly continued for at least two generations, which resulted in great population displacements among other disasters, such as storms and famine. People left their homes to live on the high hills and mountains, or nest on the trees. According to mythological and historical sources, it is traditionally dated to the third millennium BCE, or about 2300–2200 BCE, during the reign of Emperor Yao.

However, archaeological evidence of an outburst flood at Jishi Gorge on the Yellow River, comparable to similar severe events in the world in the past 10,000 years, has been dated to about 1920 BCE (a few centuries later than the traditional beginning of the Xia dynasty which came after Emperors Shun and Yao), and is suggested to have been the basis for the myth.

Treated either historically or mythologically, the story of the Great Flood and the heroic attempts of the various human characters to control it and to abate the disaster is a narrative fundamental to Chinese culture. Among other things, the Great Flood of China is key to understanding the history of the founding of both the Xia dynasty and the Zhou dynasty, it is also one of the main flood motifs in Chinese mythology, and it is a major source of allusion in Classical Chinese poetry.

The story of the Great Flood plays a dramatic role in Chinese mythology, and its various versions present a number of examples of the flood myth motif around the world. Flood narratives in Chinese mythology share certain common features, despite being somewhat lacking in internal consistency as well as incorporating various magical transformations and divine or semi-divine interventions like Nüwa. For example, the flood usually results from natural causes rather than "universal punishment for human sin". Another distinct motif of the myth of the Great Flood of China is an emphasis on the heroic and praiseworthy efforts to mitigate the disaster; flooding is alleviated by constructing dikes and dams (such as the efforts of Gun), digging canals (as devised by Yu the Great), widening or deepening existing channels, and teaching these skills to others.

Another key motif is the development of civilization and bettering the human situation despite the disaster of the deluge. During the course of fighting, surviving, and eventually getting the inundation problems under control, much progress was also made in terms of land management, beast control, and agricultural techniques. These and other developments are integral to the narrative, and exemplify a wider approach to human health and societal well being than emergency management of the flood and its immediate effects. According to legend, a comprehensive approach to societal development resulted not only in wide-scale cooperation and large-scale efforts to control the flood but also led to the establishment of the first dynastic state of China, the Xia dynasty (c.2070–c.1600 BCE).

A study on the ~1920 BCE flood published in 2016 suggested that the concurrence of these major natural and sociopolitical events known through the geological, historiographical, and archaeological records may not simply be coincidence but rather an illustration of a profound and complicated cultural response to an extreme natural disaster that connected many groups living along the Yellow River.

It was during the reign of Emperor Yao that the Great Flood began, a flood so vast that no part of Yao's territory was spared, and both the Yellow River and the Yangtze valleys flooded. The alleged nature of the flood is shown in the following quote:

Like endless boiling water, the flood is pouring forth destruction. Boundless and overwhelming, it overtops hills and mountains. Rising and ever rising, it threatens the very heavens. How the people must be groaning and suffering!