A 3 × 3 coupler demodulation algorithm was used to detect destruction along the fiber.Based on confirming the occurring of the destruction,by switching the broadband to narrowband source,Mach-Zehnder interference system works.The cross-correlation method was used to realize precise positioning,thus achieving the goal that defenders are led to stop acts of sabotage to prevent the occurrence of malice.The optical path was presented,and the detecting and locating principle was analyzed in detail.