It has been acknowledged that fertilizer, natural soil nitrogen and animal waste, municipal waste have different mass ratio of nitrogen which is presented as a symbol of δ ¹⁵N. and that the values of δ ¹⁵N for fertilizer and natural soil nitrogen and animal waste are placed less than +5‰ and higher than +10‰, respectively. thus, Nitrogen pollution sources and contribution can be interpreted in watershed through δ ¹⁵N analysis and then, analysis is performed with Kjeldhl-Dumas method. In this study, The values of δ ¹⁵N are between +1.46‰ and +8.97‰, and the nitrate concentration is placed less than 3.31mg/L and higher than 0.19mg/L, respectively. Thus, this watershed is noncontamination area at the present time. But as a result of δ ¹⁵N, contribution of natural soil nitrogen be discovered in this watershed, presently.