This paper introduces an optical fiber early-warning system based on Mach-Zehnder in order to monitor the normal operation of pipelines. Three single-mode fiber in the cable which is buried along the pipeline probe vibration signal on the ground, in which the two was not in the same casing as a sensing fiber, the formation of intervention arm, the other one as the transmission fiber, the return of the interference signal. Laser driver launched a constant wavelength of the laser to ensure the consistency, the PIN received by photoelectric conversion of light into electrical signals, and then filtering and amplify to improve the signal noise ratio. After analog to digital conversion, Judging by the energy, system located the source of danger by relevant location algorithm, and ultimately implement the function of early-warning. Experiments show that in the case of 1 km long fiber optic cable, 4MHz sampling rate, Stolen by mining the damage simulation, system can be completed within 5 s of signal acquisition and processing to alarm and positioning. after 100 times of experiments, the system did not 1 omitted, and were able to make accurate target positioning within 25 m, implement the function of early warning of pipeline safety.