Abstract: In order to study characteristics of phytoplankton community structure and its correlation with environmental factors, the species composition, the distribution and diversity of phytoplankton in the coastal waters of Caofeidian were studied based on the data collected at 14 stations in two cruises of June and September 2014. The multidimensional analysis and redundancy analysis were used to study the species composition in sampling waters and the influence of environmental factors on the phytoplankton community structure. The results indicate that a total of 62 species belong to 3 phylum and 28 genera were identified from the samples in June and September 2014. The dominant species mostly belonged to eurythermal and euryhaline and the diatoms predominated both in species number and abundance. In June, the average abundance of phytoplankton reached 111.31×10cells/m³ and the dominant species were Skeletonema costatum and Chaetoceros debilis. In September, the average abundance was 163.01×10cells/m³ and the dominant species were Skeletonema costatum and Coscinodiscus subtilis. The results of hierarchical cluster analysis and multidimensional analysis indicate that the spatial distribution of phytoplankton species in Caofeidian waters can be divided into three regions. They are the east and west waters nearby the reclamation site, the adjacent waters of Caofeidian reclamation site and the middle waters far away from the reclamation site. Furthermore, the difference of phytoplankton community composition between June and September was not significant (R=-0.997,p=0.998，n=14). The results of RDA analysis indicate that the salinity, C_DO, temperature and pH in June and the C_DO, C_PO^3-4-P, C_DIN and temperature in September were the main environmental factors affecting the spatial distribution of netphytoplankton community composition, in sequence.