Partial discharge occurs with acoustic, electrical, optical, and thermal phenomena. In the study of UHF electromagnetic signals generated by PD, it was found that different voltage levels and size structures of power equipment have an impact on the signal propagation. This article used the research ideas of UHF signals to simulate and model different voltage levels of GIL and simulated the propagation of optical signals in GIL. By observing the optical parameters on the detection planes and the detection point, the influence of voltage level on the propagation of the optical signals in GIL was studied, which provides a reference for GIL equipment manufacturing and partial discharge optical detection research.