The finite difference time domain (FDTD) method has been applied to analyze numerically the thin film bulk acoustic wave resonators in this paper. The piezoelectric governing equations and Newton′s equation of motion are discretized in spatial and temporal domain using the intermediate difference. An electrostatic field simulator named ANSOFT Maxwell 2D is used to calculate the electric field distribution and the distribution of the electric field intensity has been obtained. The distribution of every field component in spatial and temporal domain can be predicted accurately. Based on the record of the values of electrical voltage and electrical flow for a time interval, the frequency domain electrical impedance characteristics of FBAR with different electrode thicknesses are calculated by using the Prony's method.