Abstract: After impoundment and operation of Three Gorges Reservoir, algal bloom occurred sometimes in the tributaries in the reservoir area in spring and summer, impacting the water quality. A lot of studies have shown that algal bloom in reservoir tributary can be inhibited by changing hydrodynamic conditions through reservoir scheduling. In this paper, Delft3D model is used to simulate the flow in the reach from Quma to Shuangjiang Bridge of the Xiaojiang River, a tributary in the reservoir area, to study the influence of tidal dispatch on the hydrodynamic condition in the tributary and provide theoretical support for ecological dispatch. The results show that tidal dispatch of Three Gorges Reservoir can change the flow velocity of the Xiaojiang River. In general, when water level rise the flow velocity of the middle and lower reach in backwater zone decreases, the flow velocity increases when water level decrease, basically synchronously changing with the water level at the river estuary. The larger the variation amplitude of the water level during the dispatch period, the greater the disturbance of the flow velocity. During the period of water level rise, the decreasing rate of flow velocity accelerates with the increase of water level rising-amplitude, while during the period of water level decrease, the increasing rate of flow velocity accelerates with the increase of water level falling-amplitude.