An enhanced phase sensitive optical time-domain reflectometer (-OTDR) vibration sensing system based on weak fiber Bragg grating arrays is designed. A weak reflection signal from the fiber Bragg grating (FBG) with a relatively large reflectivity is used instead of the Rayleigh scattering signal in the -OTDR system. The perturbation behaviors in the optical fiber lines are determined based on the intensity variation of the interference signal between the adjacent weak FBG reflection signals and the time division multiplexing technique is used to locate external vibration points precisely. The results show that, by this system, the detection and demodulation of the vibration signal are simpler than those by -OTDR, the distributed measurement is simultaneously fulfilled, and any vibration signals in the frequency range of 10-500 Hz can be demodulated. The system has the practical application value in perimeter surveillance systems.