The arc-shaped bank erosion phenomenon in the middle and lower Yangtze River poses significant threats to flood control safety along the riverbanks.Through systematic analysis of measured data, this paper elaborates on the spatio-temporal distribution patterns and formation characteristics of arc-shaped bank erosion in the middle and lower reaches of the Yangtze River.The results show that:1)The proportion of large-scale arc-shaped bank erosion(scour-pit length≥300 m)increased substantially after the Three Gorges Project operation, rising from 21% during the pre-operation period(1973-2002)to 36% post-operation.2)The phenomenon of arc-shaped bank erosion mainly occurs during and after the flood season, and is spatially concentrated in the mainstream impingement or nearshore flows(such as curved concave banks and the heads of midstream islands).3)The formation of arc-shaped bank erosion in the middle and lower reaches of the Yangtze River is influenced by multiple factors such as nearshore hydrodynamics, riverbed boundary conditions, soil characteristics.The formation process of large-scale arc-shaped bank erosion begins with changes in local river conditions, forming nearshore deep troughs.Then, the area of the deep troughs gradually increases, and the deepest point continues to deepen and move towards the riverbank until the deep trough wedges into the riverbank.The nearshore slope is steep, and under the continuous action of nearshore water flow, the riverbank collapses.The research results can provide critical scientific basis and technical support for flood control, disaster reduction, and river management in the middle and lower reaches of the Yangtze River.