This paper focuses on the influence and mechanism of H2 in the eptaxial growth of ZnO using metal-organic chemical vapor deposition method. Studies show that hydrogen has a significant influence on the structure and properties of ZnO films. Hydrogen produces a mainly negative impact on crystal quality, surface structure, and optical properties of ZnO films when tert-butanol (t-BuOH) is used as the O sources. Raman scattering shows that hydrogen has a very good effect on the suppression of carbon contamination. When nitrous oxide is used as the O sources, the surface of ZnO films becomes smooth, and the crystal quality and optical property are improved. It is shown that hydrogen can play a positive role when N2O is used as O source. In this paper we highly estimate hydrogen's ability of reducing the surface growth energy, improving the migration of the surface atoms and the corrosion effect on the surface. Studies show that the optimization of hydrogen has a significant effect during the epitaxial growth of ZnO using the MOCVD method.