Abstract: Silicon oxide thin films have been prepared by RF-reactive magnetron sputtering method,the composition and influence of the preparing method on breakdown field were studied.The results show that the main composition is silicon oxide;The breakdown field increases with the sputtering power at first,then decreases,it reached the peak at 400 W;Compared with the film prepared on the polished silicon substrate and stainless steer substrate,the breakdown field is higher and breakdown field probability is more intense when the film is prepared on silicon