A set of easy-used calibrating apparatus for fiber-optic hydrophone′s sensitivity was invented,and a convenient measuring method of comparison was proposed.The probes of standard piezoelectric hydrophone and fiber-optic hydrophone were placed in the same sound field ,then the outputs of the two probes were linked to the digital oscilloscope for comparison measure.The research shows that the resonant peak can be removed from the working frequency range which is from 3 ~ 1000 HZ when the wall thickness of the metallic cylinder in the vibrating system is more than 10 mm or 1/10 of the cylinder′s outer diameter.Applying this setting as well as comparison method ,the calibration system is simple and the process of calibration is quick,then the error is less than 0.5 dB,which is in the demand of the calibration for fiber-optic hydrophone′s sensitivity.