A testing device for propagation characteristic of electromagnetic wave in gas insulated switchgear includes an ultrahigh frequency signal generator, a GIS testing chamber, an emitting antenna and a receiving antenna which are provided inside the GIS testing chamber. A detachable disc insulator is provided between the emitting antenna and the receiving antenna. Both terminals of a GIS testing chamber are sealed by polyurethane wave-absorbing sponge; the ultrahigh frequency signal generator is connected with the emitting antenna, and the receiving antenna is connected with a oscilloscope. A guide rod which is fixed by the disc insulator is provided in the GIS testing chamber. The present invention is capable of achieving testing propagation characteristic of partial discharge ultrahigh frequency electromagnetic wave signal of a gas insulated switchgear in a laboratory, so as to master attenuation characteristics of the partial discharge ultrahigh frequency electromagnetic wave signal.