Salt water intrusion severely threatens the water supply safety in the Yangtze River estuary. To determine the target (critical) flow rate for the scheduling of repelling salt water, we studied the mechanism of salt tide by establishing an empirical model of the relation among salinity, tidal range, and flow rate into the sea via statistical analysis. We conclude that the critical flow rate is a varying value ranging between 9 390 m³/s and 21 633 m³/s when tidal range is 290-335 cm. In response to salt water intrusion, scheduling of reservoirs in the upstream of Yangtze River alone has no significant effect as it requires large discharge and long time. In conclusion, in practice we should combine the comprehensive scheduling of the whole watershed with the storage of freshwater and repelling salt water in local reservoirs.