This paper presents the planar Fiber Bragg Grating (FBG) hydrophone probe sens- ing principle,and theoretically and experimentally researches the probe structure sensitivity, the receiving sensitivity frequency response characteristic and the acceleration response prop- erty.Planar sheet is made of stainless steel,its thickness is 0.15 mm,its diameter is 15mm,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 to 5.5 kHz.The output yielded by one unit acceleration (1 m/s~2) is equivalent to (2.52 to 3.26 Pa) acoustic pressure acting output.This probe structure is easy to form FBG hydrophone array by multiplexing technique. The research shows that this planar structure not only can form FBG hydrophone probe,but also can constitute optical FBG laser hydrophone probe.The structure can realize different bandwidth,different range acoustic pressure measurement by adjusting the geometrical size of the sheet. This paper presents the planar Fiber Bragg Grating (FBG) hydrophone probe sensitization principle, and theoretically and experimentally researches the probe structure sensitivity, the receiving sensitivity frequency response characteristic and the acceleration response prop- erty. Planar 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 to 5.5 kHz. The output yielded by one unit acceleration (1 m / s ~ 2 ) is equivalent to (2.52 to 3.26 Pa) acoustic pressure acting output. This probe structure is easy to form FBG hydrophone array by multiplexing technique. The research shows that this planar structure not only can form FBG hyd rophone probe, but also can constitute optical FBG laser hydrophone probe. The structure can realize different bandwidth, different range acoustic pressure measurement by adjusting the geometrical size of the sheet.