A metal annulus-based single cylinder mandrel structure fiber Bragg grating(FBG) vibration sensor and a phase generated carrier(PGC) demodulator based on an unbalanced Michelson interferometer are proposed in this paper.The high precision and real time signal detection are achieved for this FBG vibration sensor.Experimental results show that its resonance frequency is 388 Hz and its acceleration sensitivity is around 81 pm/g over the frequency range from 10 Hz to 200 Hz,with fluctuation at different frequencies less than 1 dB.This FBG vibration sensor is suitable for monitoring vibration signals below the frequency of 200Hz.The wavelength resolution of the demodulation system is 1.07×10-3 pm,and the acceleration resolution of the sensing system is 1.3×10-5 g.