A mechanical nonlinear piezoelectric cantilever device with multistable state is proposed in this paper. The mathematical model of the system is established by using the lumped parameter method. By analyzing the potential energy of the system, it can be seen that the system has the characteristics of multistable state with the change of system parameters. The motion state and energy harvesting performance of the system under harmonic excitation and random excitation are analyzed by using the numerical simulation method. The results show that under harmonic excitation, the system possesses good harvesting characteristics when it is in tristable state provided that the frequency of environment vibration is medium or low, whereas the frequency is high, the good one is that in solestable state. And under random excitation, the system in tristable state can move across the barrier under low noise intensity, and generate a large voltage; furthermore, the frequency of interwell motion and the output voltage will increase with the increase of the noise intensity.