To understand the features of phytoplankton communities and their main impact factors, two cruises were conducted in the coastal waters of Rizhao in February and August 2016.Phytoplankton species and dominant species composition, abundance, community diversity and environmental factors were analyzed, and the cluster analysis, multi-dimentional scaling (MDS) ordination techniques, Pearson correlative analysis were applied in this study to reveal the relationship between phytoplankton community structure and environmental factors. In total, 92 taxa were identified, which belonged to 41 genera and 3 phyla. Among them 73 were diatoms,18 were dinoflagellates,1 was Chrysophyta. The dominant species was Guinardia delicatula in winter, and Chaetoceros lorenzianus, Chaetoceros constrictus in summer.The cell abundance of phytoplankton ranged from 2.20×10⁶-6.12×10⁷ cells/m³ with an average of 2.61×10⁷ cells/m³ in winter and from 3.75×10⁴-5.70×10⁶ cells/m³ with an average of 1.22×10⁶ cells/m³ in summer.Pearson correlation analysis showed that salinity, depth of water, dissolved oxygen(DO), nitrates, nitrite, ammonium salt, total nitrogen, heavy metal (Zn) in the sea water had the great influence on abundance of phytoplankton.Compared with Shannon Wiener diversity index (H') method, multivariate statistical analysis could better reflect the water environment quality in the coastal waters of Rizhao.