In order to solve the existing problem of poor signal-to-noise ratio (SNR) in distributed optical fiber vibration sensing system based on phase-sensitive optical time domain reflectometer ( -OTDR) at the present time,a wavelet packet denoising method is given.to reduce the noise in systematic sampling sign al before other steps in this paper.Through analyzing the effective signal′s characteristics o f the system,selecting the optimal wavelet packet Sym6and comparing the different effects produced by different number of layer decomposition,three layer decomposition is chosen to reduce the noise.In the experiment,the spectr um of disturbance signal before noise reduction is compared with that after noise reductio n quantitatively,and the result proves that after noise reduction of systematic sampling signal using wavelet packet de noising,the SNR is increased in the later process of location algorithm.Through the analysis of the effective s ignal′s spectrum near vibration,it proves that the system can achieve the spati al resolution of 1m.