Abstract: In situ resistivity measurement was used to monitor oxygenation and deoxygenation processes in YBa₂Cu₃O_7-δ c-textured thin film. The results showed that the rates of in-diffusion and out-diffusion were close. The exponential relation between resistance and oxygen content was proved to be true with X-ray diffraction measurement, the activation energy of chemical diffusion was obtained to be about 0.9ev.