Flood channel is one of the important geomorphological types that exits in the estuaries worldwide. However, due to runoff一tide interaction and intensive human activities, the geomorphology of flood channel has undergone rapid variation, which is directly related to the port site selection, channel management and river regime stability. Based on the bathymetric data, hydrology and sediment records over the past 62 years, this study analyzed the morphodynamic evolution processes of the Xinqiao Channel, the largest flood channel in the South Branch of Changjiang Estuary, and its driving mechanism. The results show that the development of the Xinqiao Channel during 1958- 2020 can be divided into the following three stages. In the first stage (1958一1997)， the channel experienced cycle of“erosion- deposition” with upstream and downstream movement, and exhibited wideness and shrinkage characteristics, controlled by the coupling effect of runoff and tide. In the second stage (1997- 2003)，the channel was further suffered from erosion, extended upstream and got widely due to the impacts from the 1998 flood and 1999 flood. In the third stage (2003一2020)， due to human intervention, the northward movement of the Biandan Shoal, and runoff- tide interaction, the Xinqiao Channel moved downstream and presented shrinkage with the sedimentation center located at the upper section. In addition, the construction of the Dongfengxisha Reservoir intercepted part of the water that previously entered into Xinqiao Channel and thereby weakened the ebb tide and accelerated channel accretion, resulting in the further shallowing of the Xinqiao Channel.