Based on the theory of FEA, the model of piezoelectric circular plates was established by using ANSYS software. The effects of radius of piezoelectric vibrator, thickness of piezoelectric layer and thickness of support layer on the power output were investigated in this paper. On this basis, it discussed the features of admittance and output power of piezoelectric electric circuit. Meanwhile, the study focused on the differences between the piezoelectric bimorph in series and that in parallel. The results indicate that under the premises of high structure reliability and stable inherent frequency, in order to generate more energy, the radius of the piezoelectric vibrator should be increased and the thickness of the support layer should be minimized. The piezoelectric bimorph in series has higher output voltage and internal impedance, thus is suitable for the energy collection system with higher load impedance; while the piezoelectric bimorph in parallel has lower internal impedance than that in series, and thus is suitable for the energy collection system with moderate load impedance. When the external resistor using the two connections has optimal resistance value, the optimal output powers of the two connections are the same.