The invention discloses an NB-IoT protocol-based structure online monitoring system, which comprises a sensor module, a sensor collection and processing module, an NB-IoT data communication module, a power supply charging and power supply management module, a server side and a client terminal, and is characterized in that the sensor module obtains data through measurement, the sensor collection and processing module receives the data and sends the data to the NB-IoT data communication module; the NB-IoT data communication module is arranged at the front end, the server side is arranged at the rear end, the sensor collection processing module remotely transmits data to the server side through the NB-IoT data communication module, the power supply charging and power supply management module provides power supply, and online monitoring data display, storage and analysis management software is arranged at the server side. the monitoring data are displayed in a classified manner and stored as required, and online analysis is performed in real time, and early warning information is given. According to the invention, wiring is not needed, the cost is reduced, the power consumption is smaller, the telecom operator-level service quality can be provided, and the method can be conveniently applied to a complex structure monitoring environment.