Abstract: Tuojiang River is one of the important tributaries of the upper Changjiang River and is located in the most developed industrial and agricultural regions of Sichuan Province.However, the rapid economic development in the basin has been accompanied by a series of ecological and environmental issues, such as production and discharge of wastewater from industry and agriculture, leading to increasingly complex point and non-point source pollution.On the eve of the "15th Five-Year Plan", evaluating the spatiotemporal evolution characteristics of water quality and driving factors across the whole basin is crucial for the preparation of comprehensive basin management plans and refined management strategies.Based on the water quality data of 23 water quality monitoring sections in the Tuojiang River Basin from 2011 to 2022, principal component analysis was employed to extract the main water quality parameters affecting the water quality, and the spatiotemporal evolution characteristics and driving factors of these water quality parameters were analyzed.Results show that: ① Total phosphorus (TP) is the main pollutant exceeding standards in the Tuojiang River Basin, although there has been a positive trend in water quality in recent years.The annual variation of pollutant shows that concentrations are significantly lower in the latter half of the year, with most indicators peaking from March to May, particularly during the spring and dry season, when the pollution is most severe.② Single-factor water quality assessments reveal that the water quality of the mainstream is better than that of the tributaries, with bad pollution occurring in the Pihe River in Chengdu City at the basin upstream and other downstream tributaries such as the Fuxi River and the Weiyuan River before 2017.③ Water Quality Index (WQI) assessments indicate significant spatial differences in water quality, with poorer quality in the middle and lower reaches, while better water quality near the source of the basin.④ The analysis of driving factors shows that the extensive discharge of industrial wastewater and the application of agricultural fertilizers are the primary contributors to the poor water quality in the Tuojiang River.The discharge of industrial wastewater exhibits a spatial distribution pattern with the highest volumes in the upstream regions, followed by the middle and lower reaches, while the application of agricultural fertilizers is most pronounced in the midstream area.The findings of this study can provide a basis for relevant authorities to formulate measures for water pollution prevention and improvement.