The railway substructure needs to be monitored to determine whether the substructure is stable. In the paper, the damages to the substructure of the heavy-haul railway in the tunnel were recognized and the grouting technology and water pipes were used to avoid further damages. To monitor the state of the substructure in the tunnel, a wireless monitoring system was developed. The accelerometers, laser rangefinders, water level gauges, and cameras were used in the sensor module, the fiber optics and mobile telephony were used in data transferring module, and a data managing system was developed in the control center. To examine the measured date by the monitoring system, the measured vertical displacement and horizontal displacement, the settlement, and the water levels at the site were presented. The measured data showed that the underground voids still existed after the grouting technology and water pipes of installation were applied. The horizontal and vertical displacement and settlement were induced by the underground voids and the loading of the train. The water level varied at the three locations, and the change of the water level beneath the surface showed that the flowing water was drained due to the water pipes. The wireless monitoring system was successfully developed to monitor the real-time data of the substructure and determine if the substructures was stable.