A sound velocity measurement method based on distributed fiber optic acoustic sensing is proposedby using the sensitive property of ultra-weak fiber grating to vibration.The speed of sound is calculated bymeasuring the time dillerence of sound signals received by different ultra-weak fiber grating sensors during thesound speed transmission process.T'he method can measure the speed of sound at different temperatures with anerror of less than 0,59 between the measured and theoretieal values.lt provides a new method for soundvelocity measurement.