The reflection wavelength of Fiber Bragg Grating is sensitive to the strain and the temperature¡¦s variation. We use Fiber Bragg Grating to be the sensor head and measure the vibration frequency in constant temperature environment. The vibration of object can make the sinusoidal strain to Fiber Bragg Grating, and it will make a little phase difference to the light of the fiber. Using the interferometer and demodulation system, we can measure the phase difference and vibration frequency. Our sensor configuration is made up of imbalance Mach-Zehnder interferometer and Fiber Bragg Grating. The two light of different path need different time to pass through the vibration source, so they make phase difference. We use the demodulation circuit to measure the phase difference causing by vibration and get the vibration frequency. Our experiment structure is a novel configuration of Fiber Bragg Grating vibration sensor. Its intensity of signal is larger than the intensity of original sensor configuration, about 4dB.The novel sensor configuration is easier spread than traditional accelerometer and it is designed of all fiber. The accuracy for measuring low frequency vibration is 99.971%. The Dynamic range of the system is more than 45dB. It is larger than the dynamic range of original sensor configuration, about 9dB. The smallest signal that can be measured is about 0.0075rad.