To expand the frequency regulation range of piezoelectric motors, this paper investigates the interaction between vibration modes of piezoelectric vibrators based on the most typical rectangular plate in-plane vibration motor. Firstly, a rectangular plate piezoelectric vibrator was designed by reasonably arranging multiple groups of piezoelectric ceramic (PZT) sheets. Suitable working modes were selected, and the excitation method of these operating modes was also analyzed. Secondly, the finite element analysis software, ANSYS, was adopted to optimize the structural parameters of piezoelectric vibrator through modal analysis. Then, the optimal size parameters of piezoelectric vibrator were obtained. After that, whether the selected operating modes can be successfully motivated was verified by harmonic response analysis. Finally, the vibration characteristics of piezoelectric vibrator under conventional vibration modes and multiple modes were acquired by transient analysis, respectively. By comparative analysis of the simulated vibration displacement amplitude, the interaction between the selected multiple vibration modes can be derived.