Abstract: This paper systematically studies the hydraulic factor and sediment transportation character in the reservoir area after the impoundment of the Three Gorges Reservoir, the influencing factor to the sediment diversion ratio of the TGP. The conclusion indicated that there are three important influencing factors to the sediment diversion ratio, one is the riverbed character of the reservoir area, the other is the flow and sediment condition, and the third is the water level before dam. From June 2003 to December 2010, the sediment diversion ratio is 26.1%. The sediment discharging centers from May to October each year, during which the sediment diversion ratio is about 29.0%, especially during the flood peak time, the velocity is large, and the flow has a strong sediment transportation ability, the sediment diversion ratio is high, when the inflow discharge is larger than 30000m³/s, the highest sediment diversion ratio is 81.0%. Further more, with the rise up of the water level before dam, the sediment diversion ratio decreased, especially the capacity of coarse particle, to some extent, it affects the sediment diversion ratio, the sediment transport ability decreases with the decreasing of the flow velocity, accordingly, the sediment diversion ratio of the coarse particle decreases more evident than the total load with the decreasing of the flow velocity.