Although　the　hybrid　on-load　tap　changer　(OLTC)　maintains　the　advantages　of　arc　free　switching　and　high　reliability,　its　mechanical　structure　is　easy　to　be　damaged　and　the　electrical　stress　is　complex,　which　means　it　is　difficult　to　realize　the　electromechanical　coordination　control　in　ultra-high　voltage　(UHV)　scenarios.　In　this　paper,　a　novel　topology　derivation　and　switching　strategy　of　OLTC　for　UHV　converter　transformer　was　proposed.　Based　on　graph　theory,　the　basic　network　structure　and　combined　structure　of　tap　changer　were　obtained　by　analyzing　electrical　network.　Then,　the　network　structure　was　transformed　by　using　topology　derivation　methods,　and　network　equivalent　transformation.　Considering　the　feasibility　and　economy　comprehensively,　the　tap　switch　topology　meeting　the　actual　engineering　demand　was　obtained.　Taking　the　OLTC　based　on　star　combination　structure　as　an　example,　the　topology　derivation　process　was　introduced.　The　working　principle　of　the　six　operation　modes　and　five　switching　actions　and　trigger　conditions　for　realizing　arc　free　switching　were　investigated.　These　theoretical　results　are　in　good　agreement　with　simulation　ones,　indicating　that　the　whole　arc　free　switching　process　of　on　load　tap　changer　is　only　40ms,　and　the　loss　of　transition　resistance　is　low.　Therefore,　the　proposed　method　is　conducive　to　solving　the　problems　of　arc　burning,　additional　loss　and　electromechanical　coordinated　control　of　hybrid　OLTC,　and　has　high　engineering　application　value.　©　2022　Chinese　Society　for　Electrical　Engineering.　All　rights　reserved.