Abstract: During the long-term service of long-span steel truss girder bridges for high-speed railways, they are subjected to the coupled effects of complex loads and environments. Traditional monitoring technologies struggle to achieve real-time, accurate, and distributed structural health monitoring, making it urgent to rely on new sensing technologies to support their safe operation and maintenance decision-making. Taking a long-span three-main-truss highway-railway combined steel truss girder bridge as the engineering background, this study addresses the bridge’s characteristics such as complex structure, strong electromagnetic interference, and bearing dynamic loads from high-speed trains. Based on Fiber Bragg Grating (FBG) sensing technology, an intelligent health monitoring system integrating "sensing perception-data acquisition-storage and analysis-report generation" was constructed. The system incorporates core modules including performance perception algorithms, data denoising, and feature extraction, enabling efficient processing of dynamic signals and structural condition assessment. Field application results show that the system has a sampling frequency of 50 Hz and a strain measurement accuracy of ±1 με, which can stably capture the dynamic responses of key structural members when trains operate at speeds ranging from 250 km/h to 350 km/h. With 6 months of continuous operation, the system achieves a data validity rate as high as 98.7%, demonstrating excellent stability and reliability. FBG sensing technology is well-adapted to the complex service environment of long-span steel truss girder bridges for high-speed railways; the constructed system enables efficient monitoring capabilities, provides reliable data support for bridge preventive maintenance, and holds significant value for engineering promotion.