Abstract: In order to improve the accurate identification and diagnosis ability of abnormal working conditions of circuit breakers, a fault diagnosis method for fault free tripping of circuit breakers in railway 10kV distribution substations based on message timing diagrams was designed. By constructing a temporal logic model of tripping events, with the communication message interaction timing between the protection device and the measurement and control equipment as the core analysis object, accurate identification of tripping faults caused by secondary system implicit defects such as communication abnormalities, protection logic mismatches, and device misoperation. Extract key temporal features from multi-source messages, covering aspects such as event integrity, temporal intervals, event sequence, and synchronization; Using preset normal action logic sequences for state matching and abnormal pattern recognition, in order to quickly diagnose faults. The experimental results show that this method is significantly superior to the control method in terms of sensitivity to timing deviation detection and diagnostic response speed. It can reliably detect 5ms level timing anomalies with an average diagnostic delay of only 155.3ms, providing an effective technical solution for accurate diagnosis and efficient disposal of fault free tripping in railway distribution stations.