Nitrogen and phosphorus were important nutrients or pollutants in water. The construction of large reservoirs would have a profound impact on their transmission characteristics. Based on the measured water quality data of Huatan and Xiangjiaba hydrological stations from 2006 to 2016 in Jinsha River, the relationships between TN/Q, TP/Q and sediment concentration (S) were established, and the change characteristics of total nitrogen (TN) and total phosphorus (TP) concentrations and flux before and after Xiluodu and Xiangjiaba cascade reservoirs were studied. The result showed as follow:(1)The concentrations of TN and TP were 0.38-1.41 mg/L and 0.01-0.73 mg/L in Xiangjiaba Station, the concentrations of TN and TP were 0.32-1.33 mg/L and 0.03-0.42 mg/L before impoundment, the concentrations of TN and TP were 0.35-1.29 mg/L and 0.01-0.05 mg/L after impoundment in Xiangjiaba Station, the concentration of TP decreased by about 75% compared with that before impoundment. (2) The concentration of TN in Huatan Station was close to Xiangjiaba Station, and the concentration of TP in Huatan Station was less than that in Xiangjiaba Station before impoundment. But after impoundment, the concentration of TN in Huatan Station was less than that in Xiangjiaba Station, and the concentration of TP in Huatan Station was obviously more than that in Xiangjiangba Sation. (3)The concentration of TN in Jinshajiang River was dominated by NO₃^--N, accounting for 67.3%-91.8%. (4)The concentration of TN had a little relationship with flow and sediment concentration, and the concentration of TP had positive relationships with flow and sediment concentration. (5)The fluxes of TN and TP in Huatan Station were 48357-135827 and 4720-14163 t, with the mean values of 90337 and 8932 t, respectively. The flux of TN were 64232-130966 and 71675-149647 t, and the flux of TP were 8851-18624 and 3131-7300 t before and after impoundment in Xiajiaba Station. (6)TN concentration and discharge had no significant effect after reservoir impoundment, but TP concentration and flux were significantly reduced, the annual retention rate was about 67.0%.