Abstract: The vehicle expert diagnosis system of Nanning Rail Transit Line 5, which is composed of on-board system and ground big data center, is introduced. Based on computer, sensor, communication and industrial control technology and integration of big data and information technology, the storage, integration, analysis, display and application of on-board mon-itoring data in ground center is realized, effectively improving the intelligent level of vehicles, and the fault handling efficiency and operation and maintenance cost reduction to a further extent.