Corona　discharge　occasionally　occurs　to　the　contact　box　of　switchgear　due　to　condensation　under　high　humidity　and　pollution　conditions,　which　may　result　in　a　switchgear　insulation　fault.　In　this　article,　we　develop　an　experimental　platform　for　the　condensation　of　contact　boxes　in　switchgear.　A　metallographic　microscope　is　used　to　measure　the　size　and　distribution　characteristics　of　dewdrops　on　the　surface　of　the　contact　box　under　various　temperature,　humidity,　and　pollution　conditions.　A　simulation　model　for　the　distribution　of　dewdrops　is　established　using　fractal　theory,　and　the　simulation　results　match　the　measured　results　well.　The　corona　onset　voltage　is　predicted　and　verified　by　the　UV　imager＇s　measurements　by　substituting　the　electric　field　distribution　around　the　contact　box　with　different　dewdrops　into　the　streamer　inception　criterion.　The　research　results　indicate　that　higher　humidity　and　temperature　differences　result　in　a　larger　dewdrop　and　a　shorter　condensation　formation　time,　resulting　in　a　lower　corona　onset　voltage.　The　effect　law　is　similar　under　high　pollution　conditions,　but　the　dewdrop　is　larger,　the　condensation　formation　time　is　longer,　and　the　corona　onset　voltage　is　significantly　lower　than　under　clean　conditions.　As　a　result,　high　humidity　and　pollution　conditions　must　be　avoided　during　the　operation　of　switchgear.　©　2022　IEEE.