Abstract: Fanshantou landslide in Songyang is a medium-sized soil landslide with two sliding belts. The geological conditions are complex. After the first discovery in 2010, it has been in a period of peristaltic deformation. In July 2018, it began to adopt siphon drainage engineering. During the process of treatment and construction, a large amount of drilling water was lost, resulting in a cumulative deformation of 57 to 74 mm in the depth of the landslide until the oblique hole was cut, and the maximum width of the landslide surface crack reached 17.5 mm. After stopping drilling and starting siphon drainage, the landslide cracks stopped expanding, and the deep area displacement was controlled within 1 mm. Based on the monitoring data of the emergency rescue, this paper analyzes the bidirectional response process of moving landslide to the changes of groundwater flow field, and analyzes the mechanism of the response process by means of hydraulics and effective stress principle. It is concluded that groundwater runoff permeability must be fully considered in design calculation and engineering practice, and can not be ignored blindly.