The tailings pond at the Tonglushan Copper-Iron Mine has already been decommissioned. To ensure itslong‑term safety and stability after closure, an online monitoring system based on GNSS technology was developed,tailored to the current conditions of the facility. This paper presents the overall architecture of the monitoring system,including the design of GNSS monitoring stations, layout of monitoring points, equipment selection and installation, andthe development of an online monitoring information management system based on SOA. The system enables deformationanalysis of the tailings pond and investigates the causes of deformation. Key risk points requiring focused monitoringare identified. Application of the system has significantly improved the management level of the Tonglushan tailingspond, reduced the long‑term post‑closure monitoring and maintenance workload, and provided a valuable reference forsimilar mines.