Thickness and material of electrode and piezoelectric film of the Film Bulk Acoustic Resonator (FBAR) are main influence factors of resonant frequency, desired resonance frequency can be achieved by confirming thickness and material. A formula about thickness, material, frequency parameter and angular frequency has been achieved by deriving stress equation of motion in longitudinal wave of film bulk acoustic resonator; frequency parameter has been obtained from Newton iteration of determinant of stress and displacement boundary conditions equations simulated by the MATLAB. Determined thickness, material and frequency parameter which is obtained by Newton iteration has been substituted into formula, and the resonant frequency calculation value is 1.453 8 GHz. Equivalent circuit of longitudinal vibration Mason model which has the same thickness, material with formula calculation has been simulated by ADS, and resonant frequency of simulation model is 1.463 GHz. Verification simulation of equivalent circuit of longitudinal vibration Mason model shows that the resonant frequency calculation value by formula and the simulation value of model are very similar, and we can use the formula to calculate longitudinal wave resonance frequency of L band FBAR.