A 1D hydrodynamic model on Pengxi Backwater Area (PBA) in the Three Gorges Reservoir during its preliminary operation period (2007 2008) is set up based on HEC RAS. In the large submerged area or water fluctuation zone, virtual levee is set up in the model between the conveyance channel and the storage area. The Manning’s n in PBA is calibrated and selected in the range of 0.27〖XC半字线.tif,JZ〗0.35. Calibrated model has good modeling results. Quasi Steady simulation approach is applied to calculate 1D hydrodynamic condition in the PBA during the study period. Analysis on the hydrodynamic condition in the PBA show that in the low water level operation stage, average velocity of upper reach in PBA will exceed 0.5 m/s, which is close to natural river. The Gaoyang Lake is formed as a relative independent and semi closure dam lake in the middle reach of PBA. Due to the enlarged cross section, the velocity at downstream of PBA is significantly decreased. In the high water level operation stage, no remarkable difference of velocity among cross sections in the PBA, indicating a significant hydrological characteristic of deep river based reservoir. The variation of reservoir capacity and hydraulic retention time in the PBA is 8.26×10 8〖XC半字线.tif,JZ〗2.51×10 8 m 3 and 157.0〖XC半字线.tif,JZ〗3.8 d respectively. The variation of reservoir capacity in PBA is impacted by the water level fluctuation more significantly. The hydraulic retention time in the PBA is impacted by both and river discharge dually. Frequency analysis show that 17.8% of hydraulic retention time data in the PBA is showed to be overflow reservoir type and 82.2% of that data showed to be transition type.