GNSS technology is mainly used in deformation monitoring of high-rise buildings, reservoir dams, bridges and other buildings, as well as settlement, displacement and inclination of engineering foundation pits. For example, the Three Gorges Project in China is the largest water conservancy project in the world. Through the GNSS automatic deformation monitoring system established in the Three Gorges Reservoir Area, the monitoring data of deformation information such as settlement and landslide in the Three Gorges Reservoir Area have been obtained, which is of great significance to the safety of the Three Gorges Dam and the reservoir area. Because GNSS technology has the advantages of high precision of sub mm level, all-weather observation, no need to maintain intervisibility between stations, simultaneous measurement of three-dimensional displacement of points, and easy realization of automation of the whole system. Therefore, GNSS technology has been applied more and more in deformation monitoring, especially in large-scale projects.