Abstract: In order to explore the spatio-temporal variation characteristics of key factors in the entire process of algal blooms in the middle and lower reaches of Hanjiang River, based on the synchronous monitoring data of quantity and quality of important control sections along the main stream of the Hanjiang River from March 13 to March 21, 2024, the hydrological, water quality, and aquatic ecological characteristic indicators of each section in the entire process of algal blooms were analyzed.Pearson correlation analysis method was used to evaluate and analyze the correlation characteristics of key factors in algal blooms.The results showed that during the occurrence of algal blooms in the middle and lower reaches of Hanjiang River, there was no significant trend of daily runoff along the important control sections of the main stream, but the daily runoff of individual sections showed a decreasing trend day by day.The nitrogen and phosphorus nutrients in the Jijiazui Section showed a "lag" in growth.Even though the runoff of the Jijiazui Section decreased day by day during the algal bloom, the total phosphorus concentration increased significantly, and the dissolved oxygen saturation and algal density gradually decreased with the development of the algal bloom process.Total phosphorus, dissolved oxygen saturation, and algal density are all significantly positively correlated with runoff, and dissolved oxygen saturation was highly significantly positively correlated with algal density.During the research period, the daily runoff of the middle and lower reaches of Hanjiang River remained relatively stable.In the later stage of the algal bloom process, nutrients such as nitrogen and phosphorus in the water accumulated in the Jijiazui Section of Hanjiang River estuary.The research results can provide a reference for the prevention and control of algal blooms and water resource protection in the middle and lower reaches of Hanjiang River.