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A two-dimensional edge detection method has been proposed to extract location information of intruder in the distributed vibration sensing system based on phase-sensitive optical time domain reflectometry. The edge detection method is used to calculate the spatial gradient of the image composed by Rayleigh traces at each point by convolving with Sobel operator, hence the amplitude fluctuation of Rayleigh backscattering traces induced by external vibration can be located. The signal to noise ratio of location information based on the method increases to as high as 8.4 dB compared to conventional method, where the effects of noise are reduced by local averaging within the neighborhood of mask. The spatial resolution could be also optimized from 5 m to ~3 m when 50 ns pulse is launched into the single mode fiber with 1 Km length. The sensing system has the potential to extract available signals from the hostile environments with strong background noise.