Abstract: Oxygen isotope ratio (δ¹⁸O) of water is a valuable character for the study of water cycle and food authenticity assessment, which need accurate, convenient analysis techniques. A method of gas chromatography-isotope ratio mass spectrometry (GC-IRMS) coupled with off-line isotopic exchange equilibration was developed for the determination of oxygen isotope ratio of water. The memory effect of the syringe, the tightness of spetum-sealed sample vials, the stability of the air charging system and the influence of reaction conditions for isotopic exchange equilibration were tested. Results show that no memory effect is observed, and the method is stable and convenient for the determination with a standard deviation usually better than 0.1‰. As to accuracy, a strong positive correlation is found in the δ¹⁸O values measured by GasBench II-IRMS, and it is recognized by top isotopic analysis laboratories in Europe.