Abstract: Based on the data collected from two surveys in the coastal waters of Rizhao in May and November 2016, community structure of phytoplankton was studied and its relationships with environmental factors were performed with Pearson correlation analysis. A total of 78 phytoplankton species were recorded with 66 species of Bacillariophyta, 10 species of Pyrrophyta, and 2 species of Chrysophyta. Noctiluca scintillans, Coscinodiscus subtilis, Chaetoceros densus were dominant species.The average abundances ranged from 24.61×10⁴ cells/m³ in autumn to 69.38×10⁴ cells/m³ in spring. The average Shannon diversity (H′) , Margalef's species richness diversity (D) and Pielou's evenness index (J) were 1.56, 2.21, 0.44 in spring, respectively, and 2.99, 4.00, 0.73 in autumn, respectively. Cluster analysis showed that the phytoplankton in the area could be divided into three groups. BIOENV analysis showed that depth of water, water temperature, oils, total Soluble Solid (TSS) and metal (Zn) were main factors affecting the phytoplankton community. Further, Pearson correlation analysis showed that depth of water, water temperature, ammonium salt (NH₄-N) , total Soluble Solid (TSS) and heavy metal (Cu, Zn, Hg) were main factors affecting the abundance of phytoplankton in spring. Similarly, water depth, pH, salinity, dissolved oxygen (DO) and ammonium salt (NH₄-N) were main factors affecting in the abundance of phytoplankton autumn. This study can provide basic data for further study of phytoplankton community structure and influencing factors in the coastal waters of Rizhao.