Abstract: Dam deformation monitoring system(DDMS) which benefits from GNSS continuously operating reference system(CORS) is established.It consists of two reference stations and five monitoring stations.We design a star topology network architecture and TCP/IP protocol for real-time data stream transmission.A data processing software with the function of quality control,coordinates estimation and transformation,then accuracy evaluation and session time setting are realized.One-year operating results demonstrate that DDMS has higher stability.The probability of providing effective solutions is up to 98% without data loss,and 2-hour-session solution can achieve 1 mm,0.7 mm,1.7 mm at north-south,east-west and vertical component of station respectively.The accuracy can be improved to 0.8 mm,0.5 mm,1.4 mm respectively while the session time extends to four hour.It is concluded that the system can provide a technically advanced and cost-effective infrastructure for dam deformation monitoring analysis.