In view of the remote collection of voltage and current in the online monitoring system for dielectric loss of high-voltage capacitive equipment in substations, it will lead to the problem of difficult to guarantee collection synchronization and large data transmission. The paper cleverly borrows AC 220V voltage as the reference phase, current and voltage monitoring terminal Calculate the phase relationship between the current, voltage and the reference phase of the capacitive device, and send it to the master station as an intermediate result. The master station calculates the dielectric loss of the capacitive device and forms a demand report. This method avoids the problem that the current and voltage acquisition is difficult to synchronize, and can greatly reduce the system cost and the amount of transmitted data. Because the terminals are calculated separately, the real-time performance of the monitoring system is improved.