Silicone rubber/semi-conductive layer composite interface in cables joint was the main factor to cause the partial discharge（PD） ultra-high frequency（UHF） electromagnetic wave attenuation. Analysis on the UHF electromagnetic wave propagation characteristics of the composite interface can provide a theoretical basis for the cables joint PD UHF detection. To study the propagation characteristics of PD UHF electromagnetic wave in the cables joint

on the basis of reasonable simplification

we established a computer simulation model of silicone rubber/semi-conductive layer composite interface with external shielding layer

and set a Gauss pulse current source in the silicone rubber to simulate internal PD. Moreover

using the Finite Difference Time Domain（FDTD） method

we studied variation characteristics of electromagnetic wave in time domain and frequency domain which was traveled through the composite interface

and obtained the time domain and frequency domain waveforms of PD UHF electromagnetic wave at typical positions

and the dynamic process of electromagnetic wave propagation on the silicone rubber/semi-conductive layer composite interface. The results show that

according to the simulation model in this paper

when UHF electromagnetic wave travels through the semi-conductive outer layer and copper shield layer

the intensity has attenuation of about 50 times; and the frequency range slightly changes

but the energy peak shifts toward high frequency.