Nitrogen isotope tracing method was used to identify the dominate contamination source of Chanhe River and Laohe River. The results showed that the delta15N-NO3- values of Chanhe and Laohe River from upper to lower stream were 1.34 per thousand to 9.0 per thousand and 3.3 per thousand to 7.4 per thousand, respectively. And the delta15 N values of the sewage samples were 11.5 per thousand and 11.1 per thousand. Through comparing the upper and lower stream delta15N value with the sewage sample, this research found that nitrate isotope indicated the contamination sources, and the nitrate isotope value could provide more valuable messages relative to the nitrate concentration. Meanwhile, this research approximately divided the main nitrogen source in different river drainage areas. These results can offer important information for investigating the nitrate pollution and nutrient runoff in this area.