Abstract: Based on the data collected from Tangshan coastal waters in June and September of 2021, the characteristics of temporal and spatial distribution of phytoplankton community structure and influencing factors were analyzed. Results showed that three classes including 39 genera 79 species (forma and varieties) were identified. There were 4 dominant species of diatom and dinoflagellate in June, and 5 dominant species of diatoms in September. There were no dominant species shared in these two months. The average abundance of phytoplankton was 7.48×10⁴ cells∙m⁻³ in June and 316.99×10⁴ cells∙m⁻³ in September. Spatial distribution of the phytoplankton overall abundance showed a tendency of seaward decrease. Both cluster analysis and multi-dimensional scale analysis revealed that the phytoplankton community structure varied in June and September significantly, the species succession was obvious, and the community structure variation was greater in June than that in September. RDA analysis showed that the phytoplankton community structure in Tangshan coastal waters was mainly affected by salinity, water temperature, DIP and suspended solids. In June, the seawater was cold with high-salinity, low DIP and high suspended solids concentration; while in September, the seawater was warm with low-salinity, high DIP and low suspended solids concentration.