Abstract: The hydrodynamic models was established based on DHI MIKE3, coupled with Particle Tracking module to study the influence distances of the particles released at drain outlets and analyze the impact imposed on the water exchange of the adjacent seas of the drain outlets into the Bohai Sea by coastline and topography changes from 2004 to 2014.The numerical simulation results indicated that water exchange becomes weaker on the whole.The distance is significantly decreased in the northeast and northwest of Liaodong bay, northwest of Bohai bay and most area of Laizhou bay.Water exchange significantly enhanced in south Bohai bay mouth and Bohai strait, the variation is small where the change of coastline and topography is small.The changes of coastline and topography would influence water exchange because they influence the value and direction of residual current and produce new circulations near these areas.