A FBG accelerometer as a sensor of oscillation system demodulated by DFB laser is demonstrated.The working principle and system constitution are presented.The cantilever packaging scheme is also designed to enhance the sensitivity of the FBG sensor. The sensor's response to frequency and acceleration is measured by experiment.It is shown that the heavier the mass which attached to the cantilever is, the higher sensitivity of the sensor will be,but this will result in the lower resonate frequency.Relationship between resonance suppression and viscosity of silicone oil given and discussion about the sensor's sensitivity and wavelength of DFB laser is carried out.