Abstract: The constructions of the Coastal road and the Sandun road in the Luerhuan River of the Qinzhou Bay have caused the changes in overall morphology of the bay. In order to study the impact of the development and utilization of ocean engineering on the bay, hydrodynamic models for three periods of 2000, 2013 and 2020 are established and the data of water depth in each period are contrasted. The distribution of hydrodynamics and the changes of seafloor topography in the bay are also analyzed quantitatively. The results reveal that the Coastal road constructed in 2004 has caused the surrounding water channels to produce obvious "catchment effect". The Sandun road constructed in 2010 has made the Luerhuan River "separated" integrally and the dominant route of rising and ebb tides changed. The duration of the ebb tide in the bay has increased, the duration of flood tide has decreased and the form of the tide level curve has been changed. The dominant strong tidal current flowed in a NE—SW direction at the northern side of the Malan Island in 2000 and changed to a N—S direction along the Sandun road after 2013. The overall characteristics of the tidal current velocities along both the eastern and the western sides of the Sandun road have changed. The channel of the strong tidal current is very consistent with the changes in the position of 2 m isobaths. The general increase of tidal current velocity at the southeastern side of the Malan Island has lead to the formation of new water passage within the range of 0 m isobath. The water passage between the roadbeds of the Coastal road erodes the seabed continuously and the original deep trough has shifted eastward. All the deep troughs around the Malan Island show a "V" shape and have a trend of offset and deepening. The erosion at the eastern side of the Sandun road has lead to the development of new deep troughs with a "V" shape on the whole, and close to the position of the entrance in the south "W" shaped troughs can be found. This study is helpful for deepening the understanding of the degree of impact caused by ocean exploitation and utilization in the study area and mastering the change law of hydrodynamic characteristics and the possible changing trend of the seafloor topography in the bay and is of great significance for reconstructing the Luerhuan River scientific and reasonably in the future.