Abstract: Large-scale pipeline projects have always been crucial lifeline projects for cities, and the health monitoring of such projects has been a research hotspot. Thusly, this study combines the "digital twin" technology with the case of construction application of ultra-large-diameter flexible glass fiber reinforced plastic (GRP) sand-filled pipelines in unstable tidal flat geological areas. It develops a comprehensive and automated pipeline safety monitoring technology system based on the Internet of Things (IoT) system and on virtual simulation technology. This technology system combines limited sensor data with digital twin technology to achieve real-time monitoring and analysis of the overall safety status of pipeline projects. The paper provides a detailed introduction to the basic working principles, composition architecture, implementation process, and evaluation of monitoring effects of this monitoring system. The practical application of this system demonstrates that: by integrating various types of sensor data with simulation calculation models, the monitoring system can analyze and calculate the internal forces and deformations of the pipeline in real-time during construction and normal operation. It effectively reflects the basic safety states of internal forces, of deformations and, of settlements of the pipeline. In the construction of ultra-large-diameter flexible pipeline projects in geologically unstable tidal flat areas, the foundation form of the pipeline trench is crucial for subsequent stress and deformation conditions of the pipeline.