Abstract: Based on the field survey data near the Pearl River Estuary (PRE) in the summer of 2019, the distribution characteristics of chlorophyll a (Chl a) and nutrients in the PRE were analyzed, combined with environmental factors. The results show that Chl a and dissolved oxygen (DO) at the surface in summer are 4.192～88.209 μg/L and 4.610～10.586 mg/L in the PRE, respectively; The concentrations of dissolved inorganic nitrogen (DIN) and active phosphate (PO₄-P) and active silicate (SiO₃-Si) were 0.168～1.247 mg/L, 0.011～0.044 mg/L and 0.694～6.916 mg/L, respectively. Phytoplankton grows vigorous in the PRE in summer. According to the NEEA-ASSETS standard, 44.4% of all the stations belong to highly eutrophication (20 μg/L<Chl a<60 μg/L) , and 25% belong to excessive eutrophication (Chl a>60 μg/L) . Runoff is the main driving factor of the spatial phytoplankton distribution in the PRE in summer. Since the growth of phytoplankton in the inner area of the PRE is affected by light limitation and runoff dilution to some degree, there is no high Chl a values in the area. Consumption of phosphate by plenty of phytoplankton in the outer area of the PRE, making phosphate become a limiting factor of phytoplankton growth. Chl a was significantly negatively correlated with salinity and PO₄-P, and was significantly positively correlated with DIN and DIN/P, suggesting that the estuary diluted water exerted a significant impact on the growth of phytoplankton.