The invention discloses an optical fiber acoustic sensor and a multipoint acoustic detection device. The optical fiber acoustic sensor comprises a sensing optical fiber, an inserting core, a bushing and an energy transducing film. The end surface of the inserting core, the internal surface of the bushing and the energy transducing film form a cavity structure. Bragg gratings are engraved on the sensing optical fiber. The multipoint acoustic detection device comprises multiple optical fiber acoustic sensors. When the single wavelength laser is incident to the nth optical fiber acoustic sensor in a splitting way through an optical fiber coupler, a part of laser is reflected by the Bragg gratings to act as reference signals, and the other part of laser passes through the Bragg gratings to bereflected by the energy transducing film. When the energy transducing film is excited by the acoustic signals to vibrate, the phase of the reflected light through the energy transducing film is modulated to output detection signals. The detected acoustic signals applied to the nth sensor are acquired through the difference change of demodulating the phase of the reference signals and the phase ofthe detection signals so that multipoint acoustic measurement can be realized.