HfOxNy thin film was deposited on oxidized silicon substrate; its physical structure and chemical composition were studied in detail by X-ray diffractometer, scanning electron microscopy, field emission transmission electron microscope and X-ray photoelectron spectrometer. Microtemperature sensors with high sensitivity based on the film were fabricated. To clarify the conduction process of grain, grain boundary (GB) and the whole film, temperature-dependent AC impedances of a sensor were measured and analyzed in 40-300 K. The results show that at all of the measured temperatures, the resistance of grain is much larger than that of GB, and its rising rates with the temperature reduction are also much larger than that of GB, indicating that the resistive property of HfOxNy thin film is determined by grain. In addition, it has been confirmed that the conduction process of both the HfOxNy film and GB is dominated by thermal activation and Mott variable-range hopping (VRH) in relatively high and low temperature range, respectively. The conduction process of the grain obeys Mott VRH in the whole considered temperature range, while the Mott characteristic temperature is changed. These results provide new insights into the performance enhancement of the transition metal oxynitride-based temperature sensors.