As the information source of intelligent substation, electronic transformer needs realtime monitoring. In order to solve the problems of existing CT monitoring technology in terms of realtime performance, accuracy and storage capacity, this paper designs a set of CT side cloud collaborative realtime monitoring system based on Harmony architecture. The single chip microcomputer is used to collect the transformer data, and the GPS second pulse is used as the reference to ensure the sampling synchronization, and then the Harmony operating system is stored on the cloud, and the Kalman filter and the discrete Fourier algorithm with Cassel window are introduced on the edge computing side to filter the noise and harmonics in the process of data acquisition. When the transformer accuracy is insufficient, the buzzer alarm is triggered. Experimental verification shows that the system realizes real-time, synchronous uploading and mass storage of monitoring data of multiple transformers. The storage capacity depends on the size of cloud server and can be expanded at any time. The system meets the accuracy requirements of transformer realtime monitoring, the amplitude error is less than 0.75%, meets the accuracy level of 0.2, and allows the staff to view the results at any time and in other places. In addition, the edge-cloud collaborative working mode has the characteristics of one-time development and multi-terminal deployment, so that the system has strong portability and can be applied to other different power system scenarios.