Aiming at the problem that the optical cable is often damaged by engineering construction, a low-cost vibration early warning and positioning system for monitoring the engineering construction along the optical cable line is proposed. Multiple vibration early warning modules based on single axis Sagnac interferometer are used to monitor the vibration of multiple optical cables in real time, and the position of the vibration point is determined by the phase sensitive time domain reflectometer(Φ- OTDR) module. Experiments show that the system has low cost and good early warning effect.