Abstract: The data-driven water quality prediction model has its limitations,and is not effective in the prediction of sudden water quality abnormal events.This paper selects the monitoring section of Mashukou in the southern source of Qiantang River basin as the research object,comprehensively uses the correlation analysis method to analyze the main influencing factors of the water quality anomalies,to clarify the impact of the internal and external causes of the basin and the soil conditions on the water quality anomaly indicators,and to explore the deep reasons for the limitations of the model.The results show that the influencing factors of abnormal water quality and its coupling mechanism are complex and changeable.The abnormal turbidity is more directly affected by rainfall and runoff.The abnormal permanganate index COD_Mn is more significantly correlated with temperature and rainfull,while the abnormal changes of TP and TN are related to relative humidity,rainfull and runoff.The research results have important reference significance for improving the water quality prediction ability under the background of climate change and provide a scientific basis for the prevention and control of water pollution in natural basins.