Fiber Bragg grating (FBG) sensor monitor the micro-vibration in harsh environment is adopted. The micro-vibration cannot be detected when FBG sensor signal has low signal noise ratio (SNR) (less than 1). The averaged periodogram method is used to improve the sensitive. It divides the signal into N segments，fast Fourier transform (FFT) is performed on each data segments, then averaging the N power spectrum to get the new power evaluation. The primary results show, SNR is improved by 15.6 dB in frequency domain after the treatment with averaged periodogram method, and the FBG detection sensitivity is up to 1.5 fm. This high-accuracy sensor can be used in sustained vibration detection in structural health monitoring. It is important to increase the detection accuracy of the micro-vibration.