Based on 5 consecutive days of high-frequency measured data of flow velocity, tide level, water depth and Chlorine at three stations in upstream, midstream and downstream of the Qiantang River estuary, the salt flux for each tidal cycle was calculated by the flux mechanism decomposition method. The dynamic mechanism of saltwater intrusion under strong tide was studied. The correlation between salt flux and tidal range, the phenomenon of water and salt transport separation, and the enlightenment of anti-salt were analyzed. The results show that the salt transport in the lower reaches of the estuary is mainly controlled by the Stokes effect, while the upstream is dominated by advection transport and tidal pump transport, and the vertical shear has a very limited impact on salt transport. In the upper reaches of the estuary the phenomenon that the water body is transported downstream and the salt is transported upstream exist, which can strengthen saltwater intrusion in the upstream reaches. The net salt flux to the land has a strong positive correlation with the tidal range. The tidal range can be used as an important indicator for saltwater intrusion and anti-salt scheduling. Keywords: saltwater intrusion; flux mechanism decomposition method; tidal range; Qiantang River estuary 〖FL