The invention provides an acoustic coupler, which includes a signal modulation unit, a sound wave transmitting unit, a sound wave receiving unit, a signal demodulation unit and a package material. The signal modulation unit is used for modulating an input signal into a driving signal; the sound wave transmitting unit transmits a sound wave according to the driving signal; the sound wave receiving unit is used for receiving the sound wave to generate a sensing signal; the signal demodulation unit demodulates the sensing signal into an output signal, and the output signal and the input signal have the same waveform phase; the package material at least covers the sound wave receiving unit and the sound wave transmitting unit, so that the sound wave receiving unit and the sound wave transmitting unit are electrically isolated at least by the package material. The sound wave emitted from the sound wave receiving unit is transmitted obliquely in the package material, and is transmitted obliquely to the sound wave receiving unit after being reflected at an interface between the package material and the external air.