This study applied a nonstationary harmonic analysis(NS_TIDE)method to analyze the long-term monitoring data of 6 stations in the Yangtze Estuary, and the spatial and temporal variations of multiple sources of tidal asymmetry were quantified by a skewness metric. The results indicated that the tidal skewness shows an initial increase followed by a slight decrease as it propagates landward. The detailed amplitude variations of tidal asymmetry due to changes in the seasonal discharge were investigated. The sensitivity analysis reveals the response of tidal asymmetry to the varying discharge, which is the tidal asymmetry of upstream decreases with the increase of discharge and the tidal asymmetry of downstream shows a opposite trend. The results spanning the periods before and after the operation of the Three Gorges Dam were compared to investigate the impacts of the Three Gorges Dam. Because of the decrease in river discharge during the flood season, tides became more asymmetric at the upstream region, but a contrary trend appears at the downstream region.