As primary producers in marine ecosystems, phytoplankton play a crucial role, and their community structure dynamics are particularly important for studying the impacts of large-scale offshore wind farm construction on marine ecosystems. This study focuses on the coastal wind farm area of Jiangsu, comparing phytoplankton survey data before (2018) and after (2022) wind farm construction to analyze changes in species composition, abundance, and diversity, as well as their correlations with environmental factors. Redundancy analysis (RDA) was employed to elucidate the relationship between phytoplankton communities and environmental variables. Following wind farm construction, the number of phytoplankton species remained largely unchanged, but biomass density decreased, while the number of dominant species increased. Elevated concentrations of zinc and lead were found to inhibit diatom growth, whereas cyanobacteria exhibited higher tolerance to heavy metals. The release of heavy metals from anti-corrosion coatings on wind turbine foundations post-construction was identified as a potential key environmental driver of phytoplankton community shifts. These findings provide a scientific basis for ecological impact assessments of offshore wind farms and hold significant implications for marine ecosystem conservation and the sustainable development of wind energy.