In substation, GIS disconnector is used for transient operation, more serious very fast transient electromagnetic interference will be generated due to the slow movement of disconnector contacts and poor arc extinguishing characteristics. This transient electromagnetic interference will pose a serious threat to the electronic transformer, resulting in signal distortion and even equipment damage. This paper takes the electronic current transformer of a 252kVGIS experimental platform as the research target, starting from the mechanism of transient electromagnetic interference generated by disconnectors, obtains the electromagnetic interference source by building the equivalent circuit of GIS equipment, analyzes and determines the main interference path of the electronic transformer, builds the interference model of the electronic transformer affected by electromagnetic interference. Through simulation, it is found that the designed low-pass filter circuit has a good filtering effect on the output overvoltage signal of the Roche coil of the electronic current transformer.