A type of fiber optic hydrophone used in thin line towed array is presented. The fiber optic hydrophone, with a diameter of 13 mm, based on air-backed push-pull double armed symmetrical compensated structure is developed. Moreover, the working principle of the fiber optic hydrophone is introduced, and an optimized design structure of the fiber optic hydrophone is proposed. In the case of small diameter of the fiber optic hydrophone, the higher acoustic-pressure sensitivity is ensured, and the lower acceleration sensitivity is obtained simultaneously. Over the frequency ranging from 80 Hz to 2500 Hz, the average acoustic-pressure sensitivity of the fiber optic hydrophone is －142.5 dB with undulation of 0.8 dB, while the acceleration sensitivity is less than -20 dB. Experimental results show that the fiber optic hydrophone can well meet requirements for the use of thin line towed arrays.