Based on the statistics, analysis and comparison of the salinity, hydrology and terrain data in the Qibao Reach of Qiantang Estuary in more than 10 years, the results show that due to the influence of runoff and tidal currents, the most intensive mixing of salt-water and fresh water occurs in the reach from Zhakou to Cangqian. Strong runoff corresponds to lower chlorinity while higher chlorinity is accompanied by strong tides. The vertical and lateral distribution of chlorinity is relatively uniform, but the concentration in the main channel is greater than that in the marginal bank. Saltwater intrusion is weak in continuous wet years and continuous dry years, but it is strong in the first year of the runoff transition from abundant to dry. In spring tide, influenced by tidal wave deformation and tidal bores, flood tidal force is greater than ebb tidal force and saltwater intrusion is tend to occur. Tidal range is an important indicator of tidal power, which determines the strength of saltwater intrusion. Tidal range has indicative impacts on salt-water intrusion in estuaries.