Nitrogen pollution in groundwater is mainly caused by the intrusion of ammonium nitrogen and nitrate nitrogen. Especially when ammonium (NH₄⁺) is the major pollutant in groundwater, studying its distribution characteristics will be difficult as its migration law in aquifers is complicated and the pollutant is hard to be removed. Through boring holes at both banks of Kuihe River in Xuzhou city, we collected water samples to analyze nitrogen pollution. Test results showed that the main existence form of nitrogen in the study area was NH₄⁺, followed by NO₃^-. Isotopic analysis of δ¹⁵N-NH₄⁺ showed that 27.3% of NH₄⁺ in the groundwater was from chemical fertilizer and the rest was from the sources with high δ¹⁵N, such as animal manure and domestic sewage, etc. On the other hand, isotopic analysis of δ¹⁵N-NO₃^- showed that 15.2% of NO₃^- was from chemical fertilizer and soil organic nitrogen and 63.6% of that was from animal manure and sewage. Test and analysis of groundwater also showed that about 21.2% of samples were with higher isotope values than the pollution source, reflecting the denitrification in shallow groundwater at the study area.