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In this letter, a novel multilongitudinal mode fiber-optic vibration sensor is presented. The beat frequency of any two different laser modes is modulated by the vibration signal. The modulated beat frequency signal can be demodulated by a frequency-modulation demodulator. It is demonstrated that the vibration from 60 Hz to 20 KHz can be measured successfully. The sensor has high sensitivity and high signal-to-noise ratio, especially between 500 Hz and 7.4 KHz.