This study calculates the total phase variation of a hydrophone with a changing acoustic pressure in the sound pressure field according to the phase variation formula of the optical fiber hydrophone based on the Fizeau interference. Then, the effects of the horizontal and vertical postures and the depth of hydrophone on the acoustic sensitivity of each frequency are quantitatively analyzed through simulation. Finally, we use the vibrating liquid column method to test the experimental environment of the optical fiber hydrophone. Results show that the posture and depth factors have great influences on the final measurement results. The vertical posture of hydrophones in the frequency band of 40--2000 Hz produce a sensitivity error of approximately 0.9 dB--18.2 dB, and the sensitivity error caused by depth read deviation is within 4 dB compared those of hydrophones with horizontal posture. Owing to the acoustic pressure field difference in vertical placement conditions of hydrophone, the measured results are different from the horizontal placement results. Horizontal calibration results are more accurate than vertical results in acoustic pressure field test environment, furthermore, the measurement depth is greater, and the calibration results are more stable.