The ZnO films were deposited on quartz glass substrate by RF magnetron sputtering. The influences of the deposition power, the Ar/O2 ratio and the total press on the crystallinity of ZnO films were analyzed by X-ray diffraction. The results show that the films deposited at Ar/O2 ratio of 2:3 have better crystalline quality under our experimental conditions. The optimum power is about 120-160 W. The crystal structure was significantly influenced by the total pressure in the chamber. The total press should below 1 Pa in order to get high quality ZnO films.