Thin wurtzite (002) textured ZnO films were deposited on the quartz substrate by DC reactive sputtering with a Zn target at room temperature under different oxygen ratios. The deposition rate of the film will get slow as the oxygen ratio becomes greater. There is a turning point of the oxygen partial pressure between 20% and 30%. On the left side of the point, the deposition rate goes slower, meanwhile, the decrease of deposition rate gets even on the right side. When the oxygen ratio gets more than 30%, the oxidation of Zn is completed on the target surface. The optical properties are investigated with single oscillator model, and the grain size and stress are analyzed with X-ray diffraction. It is proved that ZnO films with good transparence and high electrical resistivity could be obtained while the oxygen ratio is more than 20%. The refractive index, spacing and stress of ZnO film will increase as the oxygen ratio increases, which is theoretically explained with the method of film growing.