Ion beam sputtering (IBS) and electron beam evaporation (EBE) are the common methods for preparing SiO2 films. The dispersive properties of SiO2 films which are prepared by IBS and EBE methods are studied in the visible and infrared regions with the methods of ellipsometry and spectrum fitting. In the visible band, the refractive index of SiO2 films is higher than bulk materials; in the infrared band, chemical defects of the two kinds of films are determined by the position of absorption. The results show that chemical defects of IBS SiO2 film are less than EBE SiO2 films, and there is only a small amount of H2O molecules and Si-OH chemical bond in IBS SiO2 films. However, besides the two kinds of defects there are other large amounts of Si-H chemical bond defects in EBE SiO2 films. This implies that there are more defects resulting from water chemical reaction in EBE SiO2 films than that in IBS SiO2 films. Therefore, the chemical defects can be effectively controlled by IBS method.