Based on FDTD numerical simulation method, the influence of the conductivity modulation on the resonant performance of ZnO bulk acoustic wave resonator, which provides guidance on the optimal design of the bulk acoustic wave amplifier, tunable filter and the detectors. The influence of the conductivity is introduced by the continuity equation. In order to improve the simulation accuracy, the fourth order Adams-Bashforth difference scheme was adopted in the continuity equation. The simulation results indicate that the resonant frequency of the ZnO bulk acoustic wave resonator can be significantly modulated by the conductivity when it is in the range of 1-30 mS/m.