Groundwater in the Qingmuguan underground river is monitored with hydrochemistry and ~N iso- tope techniques to investigate temporal and spatial variations of nitrate-nitrogen and its possible sources from May, 2010 to October, 2010. The results show that nitrate concentrations are 5. 077 mg/L at the Dingjia- longdong outlet and 0. 842 mg/L at the Tianchi inlet of the underground river. Nitrate concentrations of the groundwater are low at the Tianchi inlet, and the change range of the a~SN concentration is low, from --7. 0475 %0 to +7. 059 %0, which proves that the Tianchi inlet only polluted by nitrogen slightly and the outside influence to groundwater also slight, and the sewage and feces are not the major source of alSN in this point. The concentration of alSN at the Dingjialongdong outlet ranges, overall high and changes much more exten- sively, from --21. 453 X0 to +37. 825 %0. That proves the Dingjialongdong is affected more strongly by di- rect emission of feces from the pig farm and precipitation.