In this paper, a new method is proposed to investigate the transport mechanism of copper thin film oxidation in water vapor using H162O/H182O isotopic labeling. Copper thin films are prepared on glass substrates by vacuum deposition. The structure of copper oxide film is analysed by X-ray diffraction (XRD). The distributions of16O and18O in the oxide film are analysed by secondary ion mass spectroscopy (SIMS). The results demonstrate that the transport mechanism of copper film oxidation is short-circuit diffusion mechanism.