The hydrodynamics and water quality evolutions in response to the land reclamations in Bohai Bay were investigated by developing a coupled hydrodynamics-water quality model. Simulated results indicate reclamations considerably change the residual current fields and decrease the tidal prisms. After 1990–2006 reclamations, salinity isolines in the west of the bay obviously move towards open sea, and cause the decrease of salinity value. Compared with the 2006 reclamation scenario, the 2022 reclamation scenario generates larger salinity concentration, thereby intensifying salinity intrusion. Besides, a large amount of dissolved inorganic nitrogen (DIN) is retained in the bay and increases its concentration value due to 1990–2006 reclamations, which almost presents opposite variation in the 2022 reclamation scenario. 1990–2006 reclamations increase phytoplankton carbon concentrations in the most bay areas, with a maximum increased value of 53.37 μg/L. With the further construction of reclamations (2006–2022), phytoplankton carbon concentrations increase within several estuarine areas, nevertheless the decreases appear in the large areas from estuarine mouths to bay's center. Statistically, the averaged salinity concentration slightly changes in the whole bay, while the averaged DIN and phytoplankton carbon concentrations significantly increase by 14.92% and 13.33% during 1990–2006, then they decrease by 16.02% and 20.68% during 2006–2022, respectively.