For studying complicated riverlake relationship change after completion of TGP,a 1D steady flow wholesand mathematic model was setup. The calculations and analyses on the annual runoff at several main control stations, diverted discharges,their processes and diverted sediment at three Outlets were performed. The computed results of watersand status of Changjiang and Dongting Lake obtained from mathematic model approach to the observed data at several main hydrometric stations. This mathematic model may be used for the quantitative analysis of riverlake relationship.