In order to study the river structure evolution situation of Jingnan Three Port of Yangtze River, this paper used topography river network data of 1955, 1978, 1990, 2008 and 2016, to quantitatively analyze the changing characteristics of river network density, water surface rate, river network complexity, branch development coefficient and fractal dimension from quantity, structure and complexity, and to explore the driving factors of its change. The results show that: quantitative features: the number of rivers, the length of river, the density of river network and the water surface rate reduced, especially the low tributaries are reduced. The river network density and water surface rate of Huarong river decreased the most, of which river network density declined by 0.25 km/km2, water surface rate decreased by 4.21%; structural features: branch development coefficient declined obviously, and the most significant decrease happend on Songzi River. and its branch development coefficient K value declined 56.14%. And it also shows that river network density also declined, especially the Songzi River, and its river network complexity CR value decreased by 54.41%, which dropped from 44.98 to 20.64. It is indicated that the river network development in the region tends to be dominant and singularized; from the aspect of complexity , river network fractal dimension shows a decline trend, and the decline range of Huarong river is from 1.646 to 1.421. To sum up, the complexity of river network shows a simplified trend; the change of water and sediment time-space transportation process by river network engineering construction is the main driving mechanism of river network change.