Abstract: Based on the water quality monitoring data of Changtan Reservoir between 2010-2020, principal component analysis and factor analysis were used to determine the primary pollution sources of Changtan Reservoir. Contributions of different pollution sources to each pollution factor of Changtan Reservoir were quantified by APCS-MLR (absolute principal component score-multiple linear regression) model. Research results show that the primary pollution sources of Changtan Reservoir are endogenous pollution source, domestic pollution source and agricultural none point source. Organic pollutants and Chl-a (chlorophyll a) of Changtan Reservoir are mainly from endogenous pollution source. The endogenous pollution source contribute 75.52% of COD_Mn, 51.39% of COD_Cr, 67.00% of BOD₅ and 63.65% of Chl-a. Nitrogen mainly comes from domestic pollution source. The domestic pollution source contribute 38.54% of NH₄⁺-N, 46.80% of NO₃^--N and 77.69% of TN. Phosphorus is mainly from agricultural none point source which contributed 44.51% of phosphorus. The concentrations of TN and TP are relatively higher in Changtan Reservoir and they are mainly from external pollution sources. Lack of effective control of nitrogen and phosphorus from the pollution sources will put Changtan Reservoir at the risk of eutrophication. In the process of formulating the pollution control scheme of Changtan Reservoir, more attention should be paid on the domestic pollution source and the agricultural none point source.