The development,characteristics and cause of the tidal bore on the North Branch of Changjiang Estuary are expounded based on survey and measured data. The hydraulic jump can be distinguished using the Froude number. When the fliid tidal current velocity exceeds the propagation velocity of tidal wave, the water particles transfer the kinetic energy to the potential energy, therefore the water level abruptly jump and forms bore. Further analysis suggests that narrowed river channel increase flood current velocity and silted riverbed slows down tidal wave propagation velocity. The river channel of the North Branch of Changjiang Estuary has been narrowed and its bed has been silted for recent years because of natural processes and artificial actions, which are the main causes of increased bore frequency and strength. With the bore head advance, a great amount of saltwater and sediments flow upstream. It has profound effects on the river channel evolution and environment of the estuary.