In order to study the coupling relationship among the vibration frequency, the internal impedance, the load and the output power of the piezoelectric energy harvester, the piezoelectriccircuit coupling analysis of the piezoelectric energy harvesters with different configurations of single crystal series, double crystal series, double crystal parallel is carried out based on ANSYS APDL software. The results show that the impedance of the energy harvester exhibits a nonlinear change with the vibration frequency, which reaches the minimum value at shortcircuit resonant frequency and reaches the maximum value at opencircuit resonance. The output power of the energy harvester reaches the optimal value when the internal and external impedances match. When the damping ratio of the energy harvester is relatively small, the optimal output power appears at shortcircuit resonant and opencircuit resonance. As the damping ratio gradually increases, the optimal output power occurs between shortcircuit resonant and opencircuit resonance, and there is only one peak.