Research conclusions:(1) The existence of the old landslide mass and the relative loose earth structure were the premises of the landslide happening of landslide． As the landslide soil was weakened by seepage of the continuous rainfall，the weight of soil body increased． The high slope was formed by the earth excavation without taking the appropriate supporting measures． All these factors caused landslides when the rock and earth mass arised from the slide plane．(2) The monitoring of the deep displacement quantitatively verified that this landslide had been movable in many times with the characteristics of multilayer landslide soil． The shallow slide plane was 6.5 － 20.5 m away from the earth surface; and the deep slide plane was 15.5 － 31 m away from the earth surface． The total displacement of slide plane was 13m and the maximum deformation rate of the slide plane was 0.42 mm per day．(3) The monitoring technology for deep displacement was particularly available for the cases that the investment was limited，the geological formation was complicated and the position of sliding surface was difficult to be judged by drilling． It would play a more and more important role in the security monitoring and evaluation of the treatment effect to assist the survey and design of landslide treatment．