The tidal bore at Qinglong Harbor in the north branch of Yangtze River estuary is caused by fast tidal currents and specific river conditions. To form, the tidal current velocity must exceed the tidal wave's speed, with a large influx volume and specific channel features. When the tidal influx volume reaches a certain level, a tidal bore will occur at Lingdian Harbor, 50km upstream from the river mouth. Lingdian Harbor is identified as the initial site of the tidal bore.