Ferroelectric SrxBa1-xNb2O6 (0.2＜x＜0.8, SBN100 x＝ thin films of highly preferred c axis orientation have been grown on Si (100) substrate by the sol-gel method with post annealing at 1000°C. Investigated by x-ray diffraction and second ion mass spectrum,we observed that the SBN thin films prepared using NbCl5 precursor solution contained K+ ions, compared with Nb(OC2H5)5 precursored SBN films. By choosing appropriate contents of K+ there exists the optimum preferred orientation in SBN thin film.K ions dissolving in SBN cell and entering Si substrate can make SBN cell and Si cell a small twist simultaneously,which improves the matching of the film and the substrate to promote the high c axis superior growth.Finally,the optic characteristics of thin films have been tested.