The invention discloses a piezoelectric film bulk acoustic resonator and a preparation method thereof. The resonator comprises a substrate, an air cavity, a bottom electrode layer, a piezoelectric layer and a top electrode layer, wherein grapheme is used as the electrode layers of the device; a support layer is not needed in the structure of the device, and the air cavity is formed between the grapheme bottom electrode layer and a groove of the substrate; the piezoelectric layer is arranged on the bottom electrode layer, and the top electrode layer is arranged on the piezoelectric layer. A preparation process of a sacrificial layer is adopted, so the dependence of the traditional process on high-precision chemical-mechanical polishing equipment is overcome, the grinding time is shortened, and the flat surface of sacrificial layer is quickly obtained. The piezoelectric film bulk acoustic resonator has the advantages that the structure is novel, the high Q (quality) value and high electromechanical coupling coefficient can be obtained, and the piezoelectric film bulk acoustic resonator can be applied to the manufacturing of filters, duplexes and multiplexes in subsequent radio frequency communication systems, and can also be combined with different sensitive films to manufacture high-performance sensors.