Abstract: In order to clarify the horizontal and vertical distributions of phytoplankton community and influential factors in Caofeidian coastal waters, an investigation was conducted in August 2013. The species composition, cell density and dominant species were analyzed. The redundancy analysis (RDA) and clustering analysis were used to study the spatial variations of phytoplankton community and their relationships with environmental factors. The results showed that a total of 66 species in 34 genera of 3 phyla were identified. Bacillariophyta and Pyrrophyta were the dominant groups. The phytoplankton densities were (0.85～39.07)×10⁴ cells/L and dominant species included Nitzschia longissima, Skeletonema costatum, Eucampia zodiacus, etc. The seawater temperature, salinity and nutrients were important factors affecting phytoplankton distributions. Horizontally, cell densities showed relatively high in the inshore waters than the offshore waters, mainly caused by terrestrial nutrient inputs. Vertically, the spatial variations of phytoplankton community were observed in the offshore waters with depth exceeded 20 m. It was found that cell densities decreased with depth and most diatoms and dinoflagellates distributed in the surface waters, and benthic diatoms (e.g., Paralia sulcata) mainly distributed in the middle and bottom waters. The weakened seawater vertical mixing due to stratification was an important factor controlling the phytoplankton distributions.