The one-dimensional flow model based on Saint-Venant equation is developed.Then,it is applied to calculate the holistic hydraulic characteristics in the natural condition of the Three Gorges Reservoir in Chongqing region,which is the 500 km-long mainstream beginning at Cuntan and ending at the boundary of Chongqing.Further,the model is applied to predict the hydraulic characteristics of the calculating zone at the time of the second stage of the dam construction(156 m storage level at the dam) and the completion of the project(175 m storage level at the dam).When the reservoir is operated at the storage level of 156m,the river-width of most corss-section increasing 2 times and the cross-section average velocity is reduced by 2/3 compared with these in the natural condition.When the reservoir is operated at the storage level of 175 m,the river-width of most cross-section increasing 2.5 times and the cross-section average velocity is reduced by 3/4 compared with these in the natural condition.The validating result indicates that the model properly reflectes the holistic hydraulic characteristics.This model is an effective tool for the assessment of the environmental impacts of the Three Gorges operated at the different storage level.