Highly-oriented ZnO thin films has been successfully deposited on Si(100) by metal organic chemical vapor deposition(MOCVD) at $250^{circ}C$~$400^{circ}C$ We report on the structural properties of ZnO thin film at various temperatures and at various ratios of the he and $O_2$ gas flow rates. The crystallinity of the thin films was improved and the surface smoothness decreased with the increase of the growth temperature. In x-ray diffraction analysis with respect to ZnO(0002) peak, the full width at half maximum (FWHM) of $0.4^{circ}$ was achieved at $400^{circ}C$.