At present, fiber optic sensing technology is popularly used in the monitoring fields of bridges, tunnels and dams and has achieved good results, while the application of FBG sensing technology based on weak reflection grating is still in the initial stage. In view of the limitations of BORDR and FBG technologies in geological disaster monitoring, this paper introduces the principle of weak-reflection fiber grating sensor array monitoring technology and designs a kind of external fixed point weak-reflection grating sensing optical cable based on the characteristics of weak reflecting grating sensor array with large capacity and high precision. And then constructs a real-time landslide monitoring system by combining with weak-reflection grating sensor array monitoring technology and Internet of Things technology. This paper also carries out a calibration experiment of weak-reflection grating sensing optical cable and finally presents a field application experiment using the real-time landslide monitoring system. The monitoring system measured that the deformation of 4 consecutive weak reflection gratings from 158#-161# reached 61.91mm, which indicates that the system can accurately locate the location of the landslide displacement and monitor the size of the landslide displacement, realizing the high-density automatic quasi-distributed monitoring of the landslide geological hazard body.