According to the different ways of pollutant collection and the intersection of Tongyang Canal and tributaries, 37 monitoring points and 5 river characteristic sections were determined, and monitoring samples were taken for 4 times in non rainy period and rainy period respectively. By analyzing the δ¹⁵N value and δ¹⁸O value can be used to trace the source of nitrate, so as to distinguish the proportion of urban domestic sewage and industrial sewage, urban non-point source pollution, agricultural non-point source pollution and domestic sewage in the characteristic sections of rivers. According to the distribution law of pollution sources, three kinds of pollution load reduction schemes are designed, which have a greater reduction effect on the pollutant concentration compared with the background value. Among them, the pollutant reduction of water diversion scheme is the largest, the inhibition effect of non-point source reduction scheme on nitrate nitrogen is more obvious, and the effect of point source reduction scheme on ammonia nitrogen and total phosphorus is more significant.