Abstract: One dimensional Mason model is adopted to investigate the frequency response character of a film bulk acoustic wave resonator.The influences of electrode and AlN films thicknesses on the resonant frequency,piezoelectric constant d₃₃ and electrode to AlN thickness ratio on the effective resonator coupling coefficient are discussed.The relationship between the quality factor and resonant area and energy loss in the substrate are also studied.Frequency response character of BAW fits well with the simulation result.