Abstract: In recent years, the shoreline and bathymetry changed significantly after the reclamation projects in Sanmen Bay. It is necessary to evaluate the characteristics of tidal amplitude once again. A two-dimension tidal model is established based on ADCIRC to study the changes of tidal amplitude after the reclamation projects. The results show that the semidiurnal tide is dominant in Sanmen Bay where the tidal amplitude differed significantly between the bay mouth and the bay top. The change of shoreline by reclamation projects affected obviously the semidiurnal tidal amplitude. Thus, M2 constituent amplitude decreases from 0.08 m to 0.10 m. Here, experimental formula is used to calculate the sediment siltation by the reclamation projects. The average siltation near the reclamation projects is from 1.5 m to 2.5 m and the siltation at the deep-water zone is much higher. When the bathymetry change caused by siltation is considered, the tidal amplitudes near the reclamation engineering area are dramatically reduced and the amplitudes of semidiurnal tidal constituents decrease much more than that of diurnal tidal constituents. The amplitude of M2 tidal constituent decreases obviously in the vicinity of reclamation projects and gradually to the offshore waters. The change of tidal amplitude caused by bathymetry is much serious than that by shoreline.