Abstract: The compression deformation of the loose layer is the main factor causing the land subsidence, and large deformation will cause a series of geological disasters. In order to carry out fine observation on the compression deformation of loose layer in Tongzhou, Beijing, 112 m thick loose layer has been monitored for one and a half years by using directly buried cable. The results show that during the monitoring period, the main compressed layer of the loose layer in the monitoring area is 5~30 m. The amount of compression in this layer tends to decrease with time, and also decrease with depth. Based on the analysis, the main causes of the compression deformation of the loose layer in this area are the change of groundwater level, the additional load of construction and the characteristics of its own lithology. BOTDR technology can accurately obtain the deformation information of loose layer, and it is an effective means to monitor the compression of loose layer.