©,　2015,　Xi＇an　High　Voltage　Apparatus　Research　Institute.　All　right　reserved.　We　use　the　finite　difference　time　domain　method　to　analyze　electromagnetic　wave　propagation　characteristics　in　GIS　for　the　purpose　of　the　UHF　on-line　monitoring　of　partial　discharge(PD)　in　GIS.　Firstly,　a　model　for　detecting　PD　signals　in　GIS　is　built　according　to　the　real　experimental　device　to　study　the　influences　of　the　pulse　width　and　amplitude　of　excitation　source,　the　time　delay　characteristic　and　the　GIS　structure　on　the　electromagnetic　wave　propagation.　Simulation　results　show　that　the　amplitude　and　attenuation　speed　of　electromagnetic　wave　has　close　relation　with　the　pulse　width　and　amplitude　of　the　excitation　source.　This　feature　can　be　used　to　determine　PD　source　type　and　evaluate　PD　level.　The　propagation　of　UHF　electromagnetic　wave　signal　in　GIS　has　the　time　delay　and　amplitude　attenuation　effects,　which　is　beneficial　to　locating　position　of　PD　source.　And　GIS　structure　imposes　effects　on　both　the　amplitude　and　the　signal　characteristics　of　the　electromagnetic　wave,　therefore　sensor　should　be　properly　placed　by　considering　the　propagation　characteristics　of　electromagnetic　wave　in　order　to　obtain　better　detection.