Using the Tiaozini reclamation project as a case study, the offshore phytoplankton, zooplankton, macrobenthos, and intertidal benthos before and after reclamation were surveyed, and the variations of ecological characteristics were analyzed. The results show that phytoplankton species and biological density increased and species composition changed after reclamation; the number of zooplankton species near the reclamation area increased, and the dominant species changed; the number of benthic species decreased, with crustaceans being the main species, uniformly distributed at all monitoring stations before reclamation but only at some stations after reclamation; the number of intertidal benthos species decreased, but the dominant species were still shellfish with economic value, such as Mactra veneriformis; and the variations of biological density and biomass were small. It is concluded that reclamation changes a variety of environmental factors in the habitat, such as hydrodynamic conditions, suspended solids, and sediment characteristics, resulting in variations in biodiversity and community structure of aquatic organisms.