With the expansion of human production activities, geological disasters caused by slope instability are occurring more frequently. Hence, the research on effective monitoring and forecasting of the geotechnical stability of slopes is of great significance for the prevention and mitigation of slope geological disasters. In this study, a landslide monitoring and early warning system based on 5G Internet of Things (IoT) technology is introduced. The system monitors important indicators such as three-dimensional surface displacement, rainfall, and ground cracks using Global Navigation Satellite System equipment and various IoT sensors deployed on site. The key monitoring data are transmitted and displayed by 5G communication and advanced data visualization technologies. An early warning guideline is established by combining the surface deformation rate–time curve according to a four-level early warning method as well as embedded vector maps such as the topographic and geomorphological remote sensing map of the monitoring area, the geological section map, and the monitoring point distribution map. The system has the functions of accurate acquisition, rapid transmission, automatic search, and comprehensive analysis and is applied to the study of creep slopes of the Lianhe terraces in Youxi County, Fujian Province, with remarkable results.