Based on the monitoring data of water quality at 5 stations in Baiyangdian lake in recent 30 years, this study comprehensively applied multi-source statistical analysis methods and literature research to systematically reveal the trend of water quality evolution, influencing factors, and control measures in Baiyangdian lake. Results showed that: ①The year of 2005 and 2015 were the periods of poor water quality in Baiyangdian lake over the past 30 years. From 2022 to 2023, the water quality of the lake area remained stable at Class III, and by 2023, the water quality was at its best level over 30 years. The main pollution indicators were COD and TP in recent years. Large scale ecological water replenishment was the main reason for the significant improvement of water quality in Baiyangdian lake. ② From 2009 to 2023, the COD, TN, and TP concentrations in the Dianqu area were in significant downward trends, with annual decrease rate of 0.611mg.(L.a)_-1 ^{(α=0.01), 0.21 mg.(L.a)}_-1 ^{(α=0.01), and 0.013 mg.(L.a)}_-1 ^{(α=0.05), respectively.} ③The water quality indicators across various monitoring stations in Baiyangdian Lake can be spatially categorized into three groups, with the Nanliuzhuang station in the western region showing the poorest water quality. Eutrophication indicators are further classified into two categories, with northern sites exhibiting a higher nitrogen-to-phosphorus ratio compared to the southern sites. Over recent years, Baiyangdian Lake has become predominantly phosphorus-limited, despite being a nitrogen-polluted system overall. ④The inflow and water level are the key factors affecting the water quality of Baiyangdian Lake in recent years. From a regional perspective, targeted management strategies are necessary for different areas of the lake. In the western region, particularly at the Nanliuzhuang site, efforts should focus on controlling external nutrient inputs. In the northern sites, priority should be given to reducing total nitrogen concentrations, while in the southern sites, the main focus should be on controlling chemical oxygen demand and total phosphorus levels. Looking ahead, local authorities should intensify efforts to manage endogenous pollution, particularly from sediments and organic matter (humus) within the lake. Furthermore, a coordinated approach to pollution control across the entire watershed is essential to address both external and internal sources of contamination..