Abstract: ZnO thin films were grown on （0001） substrate by LP- MOCVD. It is found that the flow rate of O₂ influences the crystalline quality, surface morphology and PL spectrum of the as -grown ZnO thin films remarkably. With increasing the flow rate of O₂, the single -orientated ZnO thin films are degraded to polycrystalline films with the FWHM of （0002） peak broadening from 0.20℃ to 0.30℃. At the same time, the averaged grain size becomes smaller and more homogeneous, and the surface of the films is smoother. The near-band-edge emissions in PL spectrum are greatly enhanced and the deep level emissions are weakened with the increase of O₂ flow rate due to the reduction of oxygen vacancies, which suggest that the optical quality of the ZnO thin films is improved. It indicates that under our testing condition, the photoluminescenceof ZnO films is more dependent on the stoichiometry than the microstructural quality.