Abstract: In this work, to understand systematically the intensity of endogenous pollution in urban streamways, 73 sampling points were selected, the sediment stock was calculated, and the distribution characteristics of carbon, nitrogen and phosphorus in sediment and interstitial water were analyzed in a large scale area (100.8 km2), taking Suzhou water network area as the research object. Meanwhile, the changes of the water quality under water exchange, water diversion, and dredging scenarios were predicted by designing a comprehensive treatment of the water environment according to the average loads of pollutants along the rivers. The results showed that the total mass of sediment in Suzhou water network area was about 4.7×106 t, in which the average contents of TOC, TN, NH4+-N, TP and available phosphorus were 1.5%, 1270 mg/kg, 121.7 mg/kg , 1339 mg/kg and 44.4 mg/kg respectively, and 79% of the sampling points were in polluted condition. The average concentrations of TOC, BOD5, COD, TN, NH4+-N, TP and phosphate in the interstitial water of the rivers in the Suzhou water network area were 5.9, 9.6, 124.2, 12.4, 8.4, 5.9 and 0.5 mg/L respectively, and the concentrations of TP in 70% of the sampling points after 20 times dilution were belonged to class III surface water quality. Correlation analysis results showed that the partition coefficient of NH4+-N was negatively correlated with the TOC content in the sediment, and the increase of TOC content would cause NH4+-N migration from the interstitial water to the sediment. The total mass of TN in the water was reduced by 1.4 t and 1.2 t respectively and the total mass of TP was reduced by 2.4 t and 2.3 t respectively under the changing water scenario and the diversion water scenario; the total mass of TN in the water was reduced by 18.4 t and the total mass of TP was reduced by 10.1 t under the scenario of changing water after dredging; and the total mass of TN was reduced by 18.5 t and the total amount of TP was reduced by 10.2 t under diversion water scenario.  The results of this work have theoretical reference significance for understanding the sources of river pollution and designing the treatment projects in Suzhou water network area.