Abstract: A theoretical model of a vibrating electret electrostatic energy harvester for a double-ended fixed beam was established herein for a low-frequency vibration energy in the environment. The key parameters of the electrostatic energy harvester were optimized by a MATLAB/Simulink numerical analysis. The relationship between the output power, resonant frequency, and half-power bandwidth and the electret surface potential, air gap, and load resistance was also studied. The magnitude of the external excitation acceleration and the size of the electret remained constant. The numerical results are as follows:(1) the existence of an optimal surface potential makes the output power of the electrostatic energy harvester reach the maximum value. The soft spring effect gradually increases with the increase of the surface potential, making the resonant frequency of the energy harvester device shift. The bandwidth also gradually increases. (2) An optimal initial air gap maximizes the power when the surface potential is constant. The half-power bandwidth decreases as the gap increases. (3) An optimal load maximizes the power when the surface potential and the air gap remains constant. The resonant frequency is offset as the load decreases. (4) An optimal load is used to maximize the half-power bandwidth when the air gap is constant. The larger the surface potential, the greater the half-power bandwidth under the same load. Experiments show that the output characteristics of the energy harvester under different load resistances have the following characteristics:with the increase of the load resistance, the output power and the half-power bandwidth increase at the beginning, then decrease. The maximum output power is 0.188 mW when the load resistance is 90 MΩ. In addition, the half-power bandwidth reaches the maximum value of 4.7 Hz when the load resistance is 330 MΩ.