Abstract: To investigate the influence of the operation of the Three Gorges Reservoir (TGR) on the salt water intrusion (SWI) from the North Branch (NB) to the South Branch (SB) of the Yangtze River estuary (YRE), a study was conducted by analyzing salinity observations before and after the TGR operation.The results indicate that SWI from the NB of the YRE started earlier in a typical year; the intensity of SWI increased from October to November, while it reduced from December to April of the next year due to the operation of the TGR; the reduction rate of the intensity of SWI is much less than the increasing rate; during the period from January to April when SWI is the most serious and the intake of fresh water from the YRE is the most important, the reduction of SWI is not great enough, so the effect of the operation of the TGR is not significant during this period; the operation of the TGR has little effect on the reduction of SWI of the whole year, but it has reduced the intensity of the most serious SWI from the NB to SB, which can contribute to the safety of the supply of freshwater in the YRE area.