The invention provides an insulator leakage current online monitoring system. The system comprises a current monitoring unit which is used for collecting insulator leakage current, a processing unit which is connected with the output end of the current monitoring unit, and a power supply unit which is used for providing working power for the processing unit. The current monitoring unit comprises a monitoring current transformer and a current processing circuit which is connected with the secondary coil of the monitoring current transformer. On one hand, continuous online monitoring of the leakage current of an insulator can be realized to ensure that a power monitoring center can monitor the dirt condition of the insulator. On the other hand, the current transformer which is used to detect the leakage current of the insulator is well protected. The entire system can be in sustained and stable operation for a long time. The reliability of the entire power system can be ensured.