Surface　charging　phenomena　on　DC　GIL　spacers　is　a　complicated　process　affected　by　lots　of　factors,　among　which　surface　conductivity　is　an　important　dielectrics　parameter.　In　this　study,　experimental　and　theoretical　research　are　carried　out　to　investigate　the　effects　of　non-uniform　surface　conductivity　on　surface　charge　accumulation　behaviours　of　downsized　HVDC　GIL　spacers.　A　SiC/epoxy　layer　is　partially　coated　on　alumina/epoxy　spacers　to　form　a　non-uniform　surface　conductivity.　The　coating　manners　include　sector-shaped　coating　and　ring-shaped　coating.　The　accumulated　surface　charges　show　a　rising　first　and　then　decreasing　trend　with　the　increase　of　SiC　contents　in　coated　area.　When　surface　conductivity　is　high　enough,　there　is　almost　no　charge　accumulation.　Bipolar　charges,　which　are　generally　observed　on　raw　alumina/epoxy　spacers,　are　found　to　be　preferable　to　accumulate　at　interface　region　between　high　and　low　surface　conductivity.　The　orientation　of　bipolar　charges　is　determined　by　the　distribution　of　inhomogeneous　surface　conductivity.　The　formation　mechanism　of　bipolar　charges　at　the　interface　is　revealed　based　on　the　experiment　and　simulation　results.　Besides,　a　uniform　surface　conductivity　contributes　to　suppressing　randomly　distributed　surface　charges　including　bipolar　charges,　which　can　provide　guidance　for　designing　and　optimizing　highly　reliable　and　stable　HVDC　GIL.　©　2020　Elsevier　Ltd