The SiOx thin films were deposited by RF magnetron sputtering physical vapor technology on the substrates of 20μm polyethylene terephthalate（PET）, using a pure SiO2 target. An L15 (33) orthogonal experiment was designed with three factors and three values including deposition time, sputtering power, sputtering pressure. Using OTR test the effect of process parameters were researched. The primary and secondary sequence of the design parameters were acquired by the quadratic multinomial. The result showed that deposition time affected more strongly the OTR of the films than the sputtering pressure, the sputtering power affected least between them. The best SiOx thin films were prepared at a deposition time of 27.9min，a sputtering power of 1825W，a sputtering pressure of 0.3455Pa. The calculated OTR was 0.8387 cc/(m2×day)，which was consistent with the test one.