Modeling and analyzing of the piezoelectric vibration energy harvester using permanent magnets are systematically investigated to facilitate the evaluation and optimization of such a harvester. We set up a distributed-parameter model for describing nonlinear dynamic behaviors of these harvesters，and present harmonic analytical solution by using harmonic balance method. An analysis is performed using the simulation model to determine the effects of the distance between two magnets, amplitude of acceleration, electrical load resistance on the level of the output power. The optimum resistive loads under different vibration frequencies and accelerations are also compared. The results show that the bistable configuration is applicable to a small excitation case, and the closer to the transition region the small excitation position, the more the power can be harvested. Conversely, the monostable hardening configuration is suited for the large excitation case, the corresponding optimal magnet distance is not close to the transition region. Furthermore, the large amplitude oscillation between two potential wells and small amplitude oscillation within one potential well also bring forth coexisting phenomena of high-energy response and low-energy response; the closer to the transition region the oscillation position, the more obivious the coexisting phenomenon is. It is also demonstrated that exciting frequency is a decisive factor of optimum load resistance.