Abstract: The system of Si substrate and SiO2 film was researched by numerical experiment. Compared energy loss function of SiO2 film with transmission spectrum and reflection elliptically polarized spectrum of SiO2 film, TO and LO vibrational modes of SiO2 film were researched by infrared transmission spectrum and reflection elliptically polarized spectrum. In the infrared transmission spectrum with normal incidence, only TO vibrational mode of SiO2 film was found. In the s-polarized infrared transmission spectrum with oblique incidence, there was no excitation LO vibrational mode for SiO2 film. When the ncidence angle is less than 60 degree, three TO vibrational modes were all excited. When the incidence angle is more than 60 degree, three LO vibrational modes were all excited, but only two TO vibrational modes were excited. In the reflection elliptically polarized spectrum, TO vibrational mode could not be excited and only LO vibrational mode was excited. In the transmission spectrum and reflection elliptically polarized spectrum of SiO2 film, their vibrational frequencies individual shifted to long wavenumber and short wavenumber.