We have demonstrated the improvement of Hafnium oxide (HfO2) films via atomic oxygen post-treatments. The films were characterized using spectroscopic ellipsometry (SE), synchrotron X-ray reflectivity (XRR), and Doppler broadening spectroscopy (DBS) of positron annihilation radiation. The results indicated that the O deficiencies in HfO2 films greatly decreased after the treatment. It approved that atomic oxygen post-treatment is an effective method to improve the properties of HfO2 films. Moreover, the proper treatment conditions should be necessary. This research provides a new insight for the preparation of high quality oxide films.