The acoustic sensing characters of Fiber Bragg Grating (FBG) hydrophone were addressed and the relationship on FBG' s sensing character and the reflection index,grating distance and reflection wavelength bandwidth of the FBG was analyzed. By improving encapsulation structure of FBG sensinghead,the acoustic sensing-index was increased. The experiment sensing result of FBG hydrophone was compared with which of standard hydrophone and response dexterous was demarcated. The sensing signal was demodulated with demodulateonal circuit and the result according with acoustic signal was obtained.The test result indicates that at the acoustic frequency of 1 kHz～30 kHz,compared with the standard piezo-acoustic hydrophone,the frequency response of the FBG hydrophone is very flat and the SNR of output signal is good. The improved measures are in effect.