A piezoelectric generator based on the piezoelectric stack electro-mechanical energy conversion was proposed. The electro-mechanical coupling model of the generator and the relationship between the deduced voltage and the exciting force of the stack were deduced based on the piezoelectric vibration theory and one-dimensional wave theory. The effects on the power performance of piezoelectric stack physical parameters, such as the amplitude and frequency of the force, the mass and the stiffness of the mechanical system were studied. The research results show that the bigger the force, the larger the power ability, and when the frequency of the exciting force is according with the resonant frequency of the generator, the power ability of the generator is maximum. And if the length and area of the piezoelectric stack is suitable for the resonant frequency of the generator, the power ability is maximum. Moreover, if the load impedance matches the equivalent impedance of the generator, the electro-mechanical energy conversion efficiency of the generator is maximum.