Abstract: In April 2010, an investigation was conducted on the phytoplankton’s species composition, diversity, abundance, and distribution at 20 stations in the coastal waters of Dayang Port in Lüsi. A total of 85 species belonging to 30 genera and 3 phyla were identified, including 81 species and 27 genera of Bacillariophyceae (accounting for 95.29% of the total species number), 3 species and 2 genera of Cyanophyta (accounting for 3.53%), and 1 species and 1 genus of Chrysophyta (accounting for 1.18%). As for the ecotype, most of the species were of lowsalt nearshore taxa, while eurythermic and euryhalic species were rarely appeared. The main dominant species were Skeletonema costatum, Coscinodiscus marginatus, Synedra fasciculate, Nitzschia longissima, C. excentricus, Thalassiosira rotula, C. lineatus, and C. radiatus, with the dominance index being 0.319, 0.308, 0.246, 0.243, 0.186, 0.131, 0.122 and 0.120, respectively. The abundance of the phytoplankton varied from 0.641×10⁴ ind·L^-1 to 3.136×10⁴ ind·L^-1, with an average of 1.640×10⁴ ind·L^-1. The amplitude of community character indices varied greatly (species number 23-42, richness index 0.603-1.339, Shannon index 2.362-3.840, and evenness index 0.638-0.958), indicating the instability of the community structure. The mean Shannon index of the phytoplankton was 3.327, mean richness index was 1.007, and mean evenness index was 0.859. The correlation analysis showed that the evenness index was significantly negatively correlated with the water Zn and Hg contents, COD, and DIN, and positively correlated with water salinity. There were also significant positive correlations between the richness index and the water As content and DO, and significant negative correlation between the diversity index and the water Zn content.