The power pipe corridor is an important infrastructure in the city， and the monitoring and evaluation of its structure and state have attracted much attention. Aiming at the problem of external failure monitoring of power pipe corridor， this paper proposed a scheme for locating vibration events based on attenuation compensation and variance threshold of optical difference time domain curve， and proved its accuracy by experiments. This scheme was based on the phase-sensitive optical time domain reflectometry system architecture. According to the phenomenon that the optical fiber vibration caused by the broken event outside the pipe corridor leaded to a sharp increase in the confusion of the optical time domain reflectometry curve at the location of the event， the optical time domain reflectometry curve obtained from different measurement sequences was differentiated， and then the difference vector data corresponding to each position of the optical fiber was evaluated and the variance threshold was set to locate the broken event. At the same time， considering the problem that the variance threshold decreased with the increase of distance due to fiber attenuation， the attenuation compensation algorithm was used to make any scattering position on the fiber correspond to the same pulse power level， so as to correct the influence of fiber attenuation on the difference threshold. A distributed fiber-optic vibration sensing system was set up in the experiment. Optical pulses with a pulse width of 30 ns and a peak power of 30 dBm were used to obtain a positioning accuracy of ±3 m in the optical fiber range of about 25 km. The external force damage event of the power pipeline gallery has the characteristics of low frequency， strong disturbance， and long duration. The proposed system scheme suppresses Rayleigh scattering fading noise through trace averaging， and combines fiber optic attenuation compensation to correct the amplitude of the scattering signal. Therefore， the phase change of the optical signal caused by vibration events is the dominant factor in trace fluctuations to ensure that external force damage events are not missed or misreported.