To quantitatively evaluate the content of algae-derived phosphorus in Lake Taihu and the influence of the algal community structure on it, and to provide data support for a better understanding of the growth and decay of algae and the internal phosphorus cycle in the lake, this study calculated the concentration of total algae-derived phosphorus in Lake Taihu and its proportion to total phosphorus in the lake based on the monitoring data and investigation data of algae and water quality of Lake Taihu from 2021 to 2023. The results showed that from 2021 to 2023, the total algal density of Lake Taihu decreased from 6.3 × 107 cells/L to 4.4 × 107 cells/L （annual average value）, the proportion of Microcystis decreased from 79.8% to 35.6%. On the other hand, the density and proportion of cyanophyta, green algae and diatoms increased significantly, and the structure of the whole lake"s algal community changed significantly. During the same period, the total phosphorus concentration in the Lake Taihu fluctuated from 0.053 mg/L to 0.062 mg/L, and the average proportion of particulate total phosphorus was 60.4%, of which the proportion of algae-derived phosphorus in particulate total phosphorus and total phosphorus was 49.4% and 29.6%, respectively, indicating that algae-derived phosphorus is an important component of particulate phosphorus. According to the further subdivision of the algal community structure, it is found that the algae-derived phosphorus in Lake Taihu is mainly contributed by three categories including cyanobacteria, diatom and chlorophyta. From 2021 to 2022, the contribution rates of cyanobacteria to algae derived phosphorus were 66.5% and 65.7%, respectively. With the rapid decrease in cyanobacteria density in 2023, their contribution and proportion of algae derived-phosphorus also significantly decreased, while the contribution and proportion of algae-derived phosphorus from diatom increased from 23.9% to 56.1%. The total algae and cyanobacteria density in 2023 had significantly decreased compared to 2021, but due to the increase in the proportion of diatom, chlorophyta and other categories, the increase in algae-derived phosphorus provided by them compensated for the decrease in cyanobacteria algae-derived phosphorus, ultimately leading to an increase in the total algae-derived phosphorus in the entire lake instead of a decrease. Although the increase in algal density of diatom and other categories is not as significant as the decrease in cyanobacteria density, they have larger cell volume and higher monomeric phosphorus content, thus exhibiting a more significant compensatory effect on algal-derived phosphorus.