In order to harvest the acoustic energy effectively, an acoustic energy harvester with Helmholtz resonator and disc piezoelectric vibrator is proposed in this paper. The incident acoustic pressure is amplified by Helmholtz resonator and applied to the disc piezoelectric vibrator to drive the vibration motions, then the acoustic energy is transformed into electrical energy by the piezoelectric effect. The theory models of Helmholtz resonator and disk piezoelectric vibrator are established, the acousticelectric conversion principle is analyzed and the effects of the incident acoustic pressure, sound wave frequency and load impedance on the output power of the acoustic energy harvester are studied. The simulation results show that the maximum output power of the sound energy harvester is 22.86 μW and the corresponding optimal load is 578 Ω at the incident acoustic pressure of 100 dB (2 Pa) and acoustic frequency of 809 Hz.