A GIL fault on-line monitoring system based on vibration signals and support vector machine, via a monitoring device mounting on the outer surface of the CIL channel, monitors the vibration signals generated on the tube wall during the power transmission process, and perform fault diagnosis through comparison. For example, when the abnormal vibration signals appear near a certain post insulators, then it can be determined that the corresponding location is experiencing a fault. The system is capable of operating without powering off the GIL or disassembling the GIL, thus it is an economic, convenient and effective troubleshooting method with high implementation feasibility. The system can monitor the operation state of the GIL in real time and send information to a monitoring station through a wireless device, and thus guarantees the stable operation of the GIL.