ZnO thin films were grown on Si(111) substrates by pulsed laser deposition (PLD). The optical properties of the films were studied by photoluminescence (PL) spectra using a 325 nm He-Cd laser. The structural and morphological properties of the films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements, respectively. Through controlling those growth paramters, oxygen pressure, laser repetition rate, growth temperature and laser intensity, their influence on the characteristics of light emission of the ZnO thin films was studied. The optimized parameters were obtained. ZnO films with narrow full width at half maximum (FWHM) and strong ultraviolet (UV) PL peaks were acquired under conditions of about 650 ℃, 50 Pa and 5 Hz. Further more, it was suggested that UV PL peaks were due to excitonics combination, the green bands were due to the replacing of Zn in the crystal lattice for O and the blue bands were due to the O vacancies.