Abstract: Objective: In metro OCS (overhead catenary system) disconnect switch is an important component controlling electrical current flow interruption or delivery. The stable operation of the disconnect switch directly affects the accurate execution of current interruption and delivery. Therefore, the fault detection means of OCS disconnect switch device needs to be improved to identify the potential early symptoms of these faults as soon as possible, which can lower the probability of problem occurrence and reduce the emergency response of the disconnect switch device before.Method: In operation and maintenance, disconnect switch faults can be divided into mechanical and electrical faults. The disassembly analysis of most faulty parts exposes many potential hazards that are difficult to detect with the naked eye before the fault occurs in the disconnect switch device. Early detection, early warning, and early intervention can greatly reduce the occurrence of faults and improve the reliability of equipment operation. The technical route of this project is to record the currenttime curve of the switch motor opening and closing by presampling the unit in the main circuit of the motor, and then study the fault waveforms in different situations through the backend DPU (data processing unit) and compare key features, ultimately outputting abnormal results to form an earlywarning.Result & Conclusion: By simulating typical faults of disconnect switches and using oscilloscopes for design and model validation, mature and reliable industrial products are ultimately developed, greatly improving the reliability of insitu online equipment.