An acoustic resonator using a metamaterial structure having a zigzag-shaped channel has a Fabry-Perot resonance characteristic and a large refractive index. In this acoustic resonator, the sound pressure is amplified in the cavity. If symmetry is used for the zigzag shaped passage and the outlet is blocked, the acoustic pressure is further amplified and the resonance frequency is lowered. To design the acoustic energy harvesting system, a multi-physicssimulation for electrical power output is employed using the 1/4 symmetric property to reduce the computational burden, where the acoustic, structural, piezoelectric and electrical circuit analyses are fully coupled.When the piezoelectric body is mounted on the end of the designed acoustic resonator, the amplified sound pressure causes an external force to the piezoelectric body, and energy is converted to generate electricity. The efficiency of voltage and generated power increases greatly when the acoustic resonator and piezoelectric body have the same natural frequency. When the acoustic resonator and the piezoelectric body have different natural frequencies, they react more to the natural frequency of the piezoelectric body. It is shown that the proposed acoustic energy harvester outperforms one with no acoustic metamaterial.