Abstract: As technologies of state monitoring and fault diagnosis are developing rapidly, vibration monitoring as a key stability condition monitoring device, is widely used in the hydropower industry. How to extract valuable information from complex signals for decision making of maintenance, needs long-term accumulation of practical experiences. This paper describes the structure and functions of a runout monitoring system adopted for the Three Gorges power plant, together with the arrangement of measuring points and the types of sensors considered, and presents a summary on the cases of vibration diagnosis and analysis, focusing on four aspects of the system: its mechanical, electrical and hydraulic features and its basic structure. Test results and main achievements of the system are briefly discussed for better understanding of such systems and their benefits for improving signal analysis and fault diagnosis.