The invention relates to a LiNbO3/SiO2/diamond multilayer piezoelectric film and a preparation method thereof, efficiently solving the problems of the temperature stability of surface acoustic wave (SAW) devices and preparation of high c-axis orientated LiNbO3 thin film. The technical scheme of the invention is as follows: an amorphous SiO2 buffering layer is introduced between a diamond substrate and a LiNbO3 piezoelectric thin film. The preparation method comprises the following steps of: firstly, taking silicon as a target material on the diamond substrate, and depositing the amorphous SiO2 on the diamond substrate by a pulse laser deposition method to form an amorphous SiO2 buffering layer; secondly, heating the prepared amorphous SiO2/diamond substrate, taking the LiNbO3 as the target material, and depositing the LiNbO3 on the amorphous SiO2 buffering layer by the pulse lasers to form a composite piezoelectric thin film having the amorphous SiO2 buffering layer between the LiNbO3 piezoelectric thin film layer and the diamond substrate; and cooling down the layer to 18-25 DEG C after the LiNbO3 piezoelectric thin film layer is deposited. The invention has simple structure, advanced and scientific method and high temperature stability, and improves the working frequency of the SAW devices.