Aimed at the problem that the VFTO originating from operations of isolating switch in GIS may produce a fearful interference with the switch and its peripherals, a collaborative simulation method by Fieldcircuitwave of VFTO radiation interference is proposed in this paper. Combined with project living example, the GIS equivalent circuit is extracted by means of quasistatic electromagnetic field analysis firstly. Furthermore, the equivalent timevarying voltage source of VFTO can be obtained via associating the timevarying resistance model of switching arc and the broadband circuit method. Finally, using transient full wave technique in time domain, the spatial electromagnetic interference by VFTO is simulated. This method has significance for reference to the high voltage switch design.