This paper has presented a novel diaphragm-type fiber Bragg grating (FBG) vibration sensor with a small mass and an excellent sensitivity through the use of the transverse property of a tightly suspended optical fiber with two fixed ends. Two suspended optical fibers that were embedded with an FBG element each, have been arranged symmetrically along the both sides of the diaphragm in a parallel manner, and their middle points were connected with the two surfaces of the mass by rigid thin rods to sense vibration. The theoretical model of the presented sensor has been derived, and its sensing characteristics have been analyzed by numerical simulation to determine the physical parameters. Experiments have been conducted to show that its sensitivity is 31.25 pm/g within a working bandwidth range of 10~150 Hz. The linearity and relative sensitivity errors are respectively 2.21% and ±10%. The experimental resonant frequency of 300 Hz is consistent with the theoretical value, which has verified the effectiveness of the proposed theoretical model. The temperature response of this sensor has decreased to 1.32 pm/℃ in the range of 30~90 ℃ after implementing the temperature compensation. Compared with the existing diaphragm-enabled FBG vibration sensors, the proposed sensor enables to support the easy implementation of distributed measurement, and the small mass allows for detection on mass-sensitive structures.