Abstract: Based on the survey data collected in the Hangzhou Bay and its adjacent areas in April, July and October 2020, this study analyzed the spatiotemporal distribution characteristics of environmental parameters and chlorophyll a(Chl a), and explored the influencing factors of Chl a using spatial autocorrelation analysis. The results showed that the concentration of Chl a ranged from 0.20 to 41.34 μg/L, with higher values observed during summer, followed by spring and autumn. The spatial distribution of Chl a gradually increased from west to east. Environmental factors and Chl a exhibited distinct spatial clustering patterns in the southwest-northeast direction, specifically from 121.4°E to 122.2°E, in the western and eastern regions, respectively. The low concentration of Chl a in the west region was primarily attributed to light limitation caused by the high suspended matter. Conversely, the higher concentration of Chl a in the east region was influenced by the higher transparency and sufficient nutrients, creating an optimal environment for phytoplankton growth. The sharp increase in Chl a concentration during summer was attributed to phytoplankton blooms, while the significant decrease during autumn was mainly influenced by phosphorus limitation. The fluctuation of Chl a concentration in the central region resulted from varying light limitation and nutrient supply due to changes in water masses throughout different seasons. This study provides a more refined understanding of the impact of environmental factors on Chl a and deepens the knowledge of the underlying mechanisms driving spatial and temporal distribution of Chl a, as well as the causes behind red tide occurrence in the surveyed areas.