Proceeding of the Joint International Symposium on Deformatuon Monitoring. 2-4 November, 2011. Hong Kong. China. Report. In order to monitor the deformation,casued by mining coal under ground,of the main and auxiliary wells in the industry square, the monitoring network, composed of 46 monitoring points and 2 bsae points, is established. The datum session measuring of the monitoring network is adopted GPS static relative positioning method and 3 degree levelling,and the measuring results is used as Subsidence monitoring datum. The obsevation method of monitoring session is the same as datum session, but the subsidence values is computed by GQuickS software developed on the Similar Single-difference Methodology, abbreviated to SSDM, and compared with that of levelling. Analysis results show that adopting SSDM to subsidence monitoring can up to the requirement of 3 order levelling monitoring.