Abstract: We have a study about the effects of O₂ on the growth of diamond films，and the diamond films were deposited by microwave plasma chemistry vapor deposition method using CH₄/H₂ gas mixture with different concentrations of O₂ addition.The surface morphology，quality and crystal structure of diamond films were systematically characterized by scanning electron microscopy（SEM），Raman spectroscopy and X-ray diffraction（XRD）.When the O₂ concentration is in the range of 0～0.9%，the results show that with the increase of O₂ addition，the quality of the diamond films get much better.When the concentration of O₂ is increased to 0.9%，the quality of the diamond is the best，the impurity content is low，the diamond FWHM is 6.2 cm^-1 and the diamond has high crystal orientation in（111）plane.But when the concentration of O₂ is increased to 1.0%，the growth of diamond grain will be destroyed，even complete diamond films can’t be deposited.