Based on experiment and monitor principles of fiber Bragg grating (FBG) sensor,this paper focuses on monitoring the landslide under excavation and gains the surface stress change principles of the sensor.The sensing system contains many sensors set up along the slope,thus the monitoring of the internal stress of land slide can be realized.Using the standard deviation criterion of K value,the sliding law of the sl ope instability can be quantified.The experimental results show that the internal displacement changes monitored by th e FBG are consistent with the theoretical results,demonstrating that FBG can be us ed to accurately monitor the landslide and warn the slope instability by monitoring the micro changes of internal displacement.