Abstract: This paper presents the seasonal community composition of net-collected phytoplankton near the sea area of Lianyungang. The samples were collected in January (winter), April (spring), August (summer) and November (autumn) in 2014～2015. A total of 8 phyla, 68 genera, and 155 species were recorded including 115 diatom species and 30 dinoflagellate species, and other rare species such as Euglenophyta, Chrysophyta, Cryphophyta, Cyanophyta, Chlorophyta and Xanthophyta. The phytoplankton abundances in winter (230.13×10⁴ cells/m³) was significantly higher than those in spring (24.67×10⁴ cells/m³), summer (119.78×10⁴ cells/m³) and autumn (90.25×10⁴ cells/m³). Chaetoceros densus, Skeletonema costatum, Prorocentrum triestinum, C. castracanei, and Leptocylindrus minimus were the main dominant species. Both the phytoplankton community parameters (abundance, species number, Shannon-Wiener diversity, Pielou evenness, and Margalef richness index) and the environmental variables (temperature, salinity, pH value, DO, suspended solids, COD, DIN, and PO^3-₄-P levels) are seasonally different. The seasonal and spatial distributions of net-collected phytoplankton community are significantly different according to the results of cluster, multidimensional scaling and similarity analysis. Redundancy analysis shows that nutrition (DIN and PO^3-₄-P), salinity, DO, and COD are the main factors influencing phytoplankton community in turn. Since 1980s, the environmental factors in the study area had changed obviously: concentrations of NO^-₃-N dramatically increased from 1.30μmol/dm³ in 1983~1984 to 24.58μmol/dm³ in 2014～2015; and N:P ratio also increased from 8.3 in 1983～1984 to 91.9 in 2014～2015. The community structure has also experienced variation since 1980s. Combined with the historical data, we found that the dominant species of phytoplankton are shifting from diatoms alone to dinoflagellates and diatoms.