As an important component of the material and energy cycle of lake ecosystem, phosphorus is commonly used as an important control index of lake eutrophication. To probe into the relationship between eutrophication and human activities in Lake Taihu, and to grasp the spatiotemporal variation of total phosphorus (TP) concentration and its driving factors, this paper collected the data of TP concentration in Lake Taihu (1980-2020) from Taihu Basin Authority, and analyzed its spatiotemporal and annual variations characters. The results show that at the beginning of rapid economic and social development in the 1980s, wastewater discharge and the load into Lake Taihu increased accordingly with the rapid development of consumption of industrial and tertiary production. As a result, the TP concentration of Lake Taihu grew sharply from 1985 to 1995, reached a peak in 1995, then declined gradually with the incessant implementation of control and protection measures, and finally entered narrow fluctuation after 2009. The spatial distribution of TP concentration in different periods reflected pollutants inputs into Lake Taihu. The driving factors that may affect TP variations in Lake Taihu in 1980-2020 were further discussed, i.e. the impacts of wastewater discharge and water yields for economic and social development, TP concentrations within inflow rivers, external TP load, cyanobacteria bloom, water temperature, the changes of macrophytes area, sediment release, residence time etc. The results indicated that the increases of TP load, cyanobacterial blooms and water temperature, and the shrinkage of macrophyte area are the main factors causing TP concentration increase in Lake Taihu in recent 10 years. Statistics revealed that during 2008-2019, the net TP load of Lake Taihu increased by 33.9% as compared with that of 1998-2007. Moreover, the residence time of whole Lake Taihu shortened by 17.7% in the past 10 years, which probably counteracted the adverse effects affecting the TP concentration increase in Lake Taihu. Therefore, targeted measures such as source control and pollution intermission, water resource saving and emission reduction, water resources regulation, ecological restoration and dredging of contaminated area should be actively carried out in the near future governance in order to achieve better TP concentration control effect in Lake Taihu.