Abstract: In view of the difficulty of fault diagnosis of signal equipment in field of rail transit signal system, this article designed a general online diagnosis system based on protocol configuration. The system adopted XML file protocol configuration technology, implemented data analysis and personalized data display according to different configuration protocols, and has been applied in many subway projects. The application results show that the design method reduces the number of iterations of the diagnostic system, saves the development cost, and effectively improves the applicability and flexibility of the diagnostic system.