Abstract: Lake Wuliangsuhai is a typical recession lake in agricultural irrigation area, which is of great significance to the ecological protection of the Yellow River Basin. Based on the analysis of δ¹⁵N and δ¹⁸O of nitrate in agricultural drainage and lacustrine water in the Wuliangsuhai Basin, the contribution of production and domestic sewage, soil nitrogen, chemical fertilizers and atmospheric deposition was estimated by using the IsoSource isotope model. The results showed that the range of δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^- in the Lake area was from -2.50‰ to 18.17‰ and -12.02‰ to 45.09‰ respectively. The δ¹⁵N-NO₃^- value was positive summer, negative in winter, the δ¹⁸O-NO₃^- value was positive in autumn. The nitrate mainly came from agricultural activities related to chemical fertilizers and soil nitrogen in Lake Wuliangsuhai in spring, with a contribution rate of 43.7%. The nitrate mainly came from the production and domestic sewage in summer, autumn as well as winter, with the contribution rates of 51.3%, 38.8% and 40.2%, respectively. And the contribution rate of agricultural activities in summer was more than 40%, and the contribution of atmospheric precipitation was also important in autumn. The results also showed that the agricultural non-point source pollution control should be strengthened in the water receiving areas of the seventh and eighth drainage ditches in spring, since the nitrate in Lake Wuliangsuhai in spring mainly came from these ditches. The urban and rural domestic sewage treatment should be strengthened in the water receiving areas of the fifth and seventh drainage ditches in summer and autumn, because the nitrate in Lake Wuliangsuhai in spring mainly came from these ditches.