There exists several differences during the composition of stable isotpes in different environment, nitrogen isotope is a good pollutant indicator. In the monitoring of ecosystem pollution, 15N can be used as the indicator of enviromental pollution. Ecologist will determine the changeable ecological process by using the technology of stable isotope without disturbing the natural state and elementary properties of ecosystem. Stable isotope 15N can be used in mensurating the relative obtained nitrogen proportion of plant by fixation or absorption NH4+ and NO3-  in the soil, confirming the turnover rate of carbon and nitrogen, judging the source of N2O (nitrifying bacteria or denitrifying bacteria), determining of the length of food chains, ascertaining  the pollutant sources in air and water, and defining the distribution area of plant.