Abstract: The trace gas preconcentration device-isotope ratio mass spectrometer (TGC-IRMS) is the main instrument for the determination of carbon, nitrogen and oxygen isotope ratios of trace carbon dioxide, methane and nitrous oxide in gas and water samples. It has the characteristics of high sensitivity and high accuracy, and is widely used in atmospheric science, environmental science and geochemical research. The correct use, maintenance and scientific management of the instrument is the basis and guarantee for obtaining good test data, improving the efficiency of the instrument and extending the service life of the instrument. The working principle and operation flow of TGC-IRMS for the determination of nitrogen and oxygen isotope ratios of nitrate in water samples were introduced, and some countermeasures were put forward for the common problems in the use of the instrument. In addition, routing maintenance and precautions during the use of TGC-IRMS were also described.