Abstract: Based on the data collected from 30 stations in the coastal areas of Bohai bay in May and September in 2013, the phytoplankton community structure was analyzed.The results showed that 47 phytoplankton species were identified in the spring and 70 species in the autumn with diatoms and dinoflagellates dominated in both seasons.In the spring, Noctilucas cintillans, Coscinodiscus spp., Coscinodicus oculus iridis were the dominant species, where as Coscinodiscus spp., Ceratium fusus, Alexandrium catenella dominated in the autumn.Compared with the historical data, diatoms was still the dominant species in this study, but the ratio of dinoflagellates increased with the cell abundance of Ceratium furca, Ceratium fusus, Ceratium tripos, Noctilucas cintillans been increased especially.Moreover, the spatial distribution of phytoplankton cell abundance was mainly determined by the diatom with the higher values accumulated in the Haihe River estuary.