In order to calibrate the sensitivity of fiber grating hydrophone, a calibration technique of fiber grating hydrophone was studied. In this paper, the working principle of fiber grating hydrophone was introduced firstly. Secondly, using tunable laser and intensity modulation method with workpoint controlling, the signal demodulation and stably measurement of fiber grating hydrophone was realized. Based on these methods, a calibration system of fiber grating hydrophone was established using comparison methods, and its calibration frequency range was 20 Hz to 10 kHz. Finally, using this calibration system, the sensitivity of a fiber grating hydrophone made of equivalent phase shift fiber Bragg grating was calibrated in the frequency range 20 Hz to 10 kHz, and measurement uncertainty of the system was estimated. The results proved that this system can correctly calibrate the sensitivity of fiber grating hydrophone, with its expand uncertainty (at k=2) of 0.9 dB.