In order to reasonably evaluate the effectiveness of ultrasonic and UHF sensor detection in GIS partial discharge on-line monitoring, it is necessary to study the propagation characteristics of partial discharge ultrasonic and UHF signals in GIS cavity. In order to study the propagation path, diffusion attenuation law, transmission and loss of ultrasonic signals in the cavity, the GIS model was built by COMSOL finite element simulation software and the acoustic simulation of ultrasonic propagation characteristics was carried out. In order to study the propagation attenuation characteristics of UHF signals, the simulation software XFDTD is used to analyze the model through the finite difference time domain principle. It is concluded that the ultrasonic wave propagates and attenuates obviously between different gas chambers, and there is an order of magnitude difference between the ultrasonic sound pressure inside and outside the metal cavity. With the increase of the distance between the basin insulator and the PD source, the effect of the insulator on the signal attenuation is weakened. The research results can provide guidance for the on-line monitoring of ultrasonic and UHF signal detection in GIS partial discharge.