Abstract: This paper puts forward the planar Fiber Bragg Grating (FBG) hydrophone probe sensing principle, theoretically and experimentally researches the probe structure sensitivity, the receiving sensitivity frequency response characteristic and the acceleration response property. Planar circle sheet is made of stainless steel, its thickness is 0.15 mm, its diameter is 15 mm, and the length of hollow circular shell is 20 mm. For this size of the structure, the probe structure sensitivity is up to 23 fm/Pa, which is about 7300 times of the value of the bare fiber. The resonance frequency is 6.5 kHz, and the amplitude-frequency curve of the receiving sensitivity response is relatively flat within the frequency range of 100 Hz-5.5 kHz. The output yielded by one unit acceleration(1 m/s^2) is equivalent to (2.52-3.26 Pa) acoustic pressure acting output. This probe structure is easy to form FBG hydrophone array by multiplexing technique. Research shows that this planar structure not only can form FBG probe, but also can constitute optical FBG laser probe. The structure can realize different bandwidth, different range acoustic pressure measurement by adjusting the geometrical size of the sheet.