A sensor solution for weak vibration based on Fiber Bragg Grating Fabry-Perot (F-P) cavity is designed and experimentally demonstrated,in which a laser with single-frequency is used as the light source.The F-P cavity is affixed to the cantilever structure of even distribution of strain along the axis and the pair of fiber Bragg gratings as the cavity reflectors is placed freely.The vibration spreading to fiber grating F-P cavity through the cantilever beam vibration,causes changes in cavity length,thus changing the reflective light intensity of fiber grating F-P cavity.Theoretical analysis indicates that,the amplitudes and frequencies of vibration can be measured by demodulating the peaks and frequencies of the signal.The experimental results of measuring artificial vibration simulated with PZT agree with the theory well.This sensor has high measuring accuracy and can be used for detecting weak vibration.