Abstract: The Changjiang River is the mother river of the Chinese nation and a lifeline for sustainable economic and social development in China. As the impacts of global change become increasingly evident, particularly intensive human activities such as rapid economic growth of economics, urbanization, water control infrastructures, etc., the water cycle within the Changjiang River Basin is undergoing significant changes, which in turn affect the green development of the Changjiang River Economic Belt. A thorough analysis of the mechanisms and driving factors underlying the hydrological cycles and environmental evolution is of great importance for promoting green development and ecological protection of the Changjiang River. Since the 1980s, the water cycle of the Changjiang River Basin has changed significantly under the dual pressures of climate change and intensive human activities. Reservoir operations have reshaped runoff regimes. Urbanization has led to notable alterations in surface hydrological processes in urban areas and water security demands. Under extreme flood and drought conditions, a complex interactive relationship of "regulation-response-feedback" has emerged between the upstream and downstream water security coupling relationship. This paper systematically summarizes key findings in three areas, including the regulatory effects of mega reservoirs, the hydrological impacts of urban agglomerations, and the evolutionary changes of the basin-scale water cycle. The research shows that: ① Reservoirs have played a notable role in redistributing water resources by regulating floodwaters and supplementing dry-season flows, significantly altering natural runoff regimes. However, their flood reduction capacity may diminish due to increased extreme event frequency under future climate change. ② Urbanization has led to an expansion of impervious surfaces, intensifying urban heat island and rain island effects, and exacerbating conflicts between flood control from upstream reservoirs and stormwater pumping of the urban agglomerations along the main stream. ③ Under the combined influences of climate change and urban population growth, pressure on water resource security in urban agglomerations continues to rise, though future pressures are projected to ease due to projected water resource increases and population declines. This research provides scientific and technological support for the green development of the "human-water-city" system in the Changjiang River Basin and for the broader ecological protection of the Changjiang River.