Systematic indoor physical model experiments of a flat flume system were carried out to explore the influence of inland fresh water discharge on seawater intrusion in coastal reservoirs. The results show that a logarithmic decrease relationship between the invasion length of the lower saltwater wedge and the discharge of inland fresh water exists. The decrement of the invasion length of the lower saltwater wedge decreases with the increasing fresh water discharge. Compared with the groundwater, the surface water has a more significant inhibition effect on seawater intrusion in coastal reservoirs. When the discharge of inland fresh water increases, the salinity decreases at the bottom of coastal reservoirs, and the upper saltwater wedge decreases and disappears earlier than the lower saltwater wedge. Reduction of groundwater exploiting and application of water transfer into the reservoir can suppress saltwater intrusion and relieve watersalinization.