Isotopes play an important role in agriculture,medicine,military weapons,energy and environment,et al.so the detection of isotopes is particularly important.A new method of isotope identification based on reaction microscope spectroscopy is presented in this paper.The nitrogen and oxygen are the basic elements that make up the main components of air and they play an important role in all kinds of life activities. Because nitrogen and oxygen have stable isotopes and significant isotopic effects in nature,the determination of their isotopes is very important. In this paper,nitrogen and oxygen are selected as target gases to carry out electron collision experiments with the help of the third-generation reaction spectrometer,namely the reaction microscopic imaging spectrometer.Isotopes in the target gases of nitrogen and oxygen are successfully determined,and the same isotope abundance ratio as in nature is obtained in the results,which verifies the reliability of isotope determination by the reaction microscopic imaging spectrometer.The ability to distinguish isotopes with only one difference in mass fraction also demonstrates the extremely high measurement accuracy of current reaction spectrometer devices.