We demonstrate a distributed optical fiber sensing system based on the Michelson interferometer of the phase sensitive optical time domain reflectometer (φ-OTDR) for acoustic measurement.Phase,amplitude,frequency response,and location information can be directly obtained at the same time by using the passive 3×3 coupler demodulation.We also set an experiment and successfully restore the acoustic information.Meanwhile,our system has preliminary realized acoustic-phase sensitivity around-150 dB (re rad/μPa) in the experiment.