Abstract: The river regime of the Tongzhousha shoal is controlled by both the actions of the river runoff and tidal current. There are many shoals and ditches existing in the river, and a rapid evolution by erosion and deposition makes the channel boundary conditions become unstable. Using a three-dimension mathematical model, the analyses of the diversion ratio of flow and sediment in flood and dry seasons and the water-sediment exchange characteristics along the shoal-ditch section were carried out. The analysis results indicate that the east waterway is the main channel. During the ebb tide, the upstream diversion ratio is about 90%, and the diversion ratio decreases by 75% at the downstream. The diversion ratio is about 70% in the downstream, and increases by 85%~ 90% during the flood tide as a result of the overflow from the west waterway. During the ebb tide, the sediment diversion ratio, comparing corresponding diversion ratio, increases in both flood and dry seasons. In contrast, the diversion ratio of sediment during the flood tide in the flood season decreases, comparing corresponding diversion ratio, while no significant changes are found during the dry season. The same water-sediment exchange characteristics are found along the left side at the lower Tongzhousha shoal, and the primary transport direction is from the ditch to the shoal, and there is a smaller water-sediment exchange flux at the right side of the Langshansha shoal.