In　this　paper,　the　thermodynamic　analysis　of　the　lead-cooled　fast　reactor　composing　recompression　supercritical　carbon　dioxide(S-CO2)　Brayton　cycle,　steam　Rankine　cycle　and　He　Brayton　cycle　as　power　block　is　introduced.　The　advantage　of　lead-cooled　fast　reactor　composing　recompression　S-CO2　Brayton　cycle　is　explored　through　comparing　the　optimal　thermodynamic　performance　of　recompression　S-CO2　Brayton　cycle　with　that　of　conventional　power　cycles.　In　order　to　improve　the　performance　of　S-CO2　cycle,　the　recompression　supercritical　carbon　dioxide/transcritical　carbon　dioxide(S-CO2/T-CO2)　combined　cycle　is　primarily　constructed　by　using　T-CO2　as　bottom　cycle.　The　influences　of　the　turbine　inlet　temperature,　turbine　inlet　pressure　and　the　compressor　inlet　temperature　of　the　top　cycle　on　the　combined-cycle　performance　are　further　invesitgated.　Finally,　the　performance　of　the　S-CO2　cycle　and　that　of　S-CO2/T-CO2　combined　cycle　are　compared.　The　results　are　indicated　as　follows.　First,　the　lead-cooled　fast　reactor　comprising　recompression　S-CO2　Brayton　cycle　has　higher　efficiency　than　the　conventional　systems.　Second,　the　thermal　efficiency　and　exergy　efficiency　of　the　S-CO2/T-CO2　combined-cycle　can　be　maximally　improved　by　4.8%　and　8.3%　comparing　to　that　of　S-CO2　cycle,　separately.　Third,　the　thermal　performance　of　the　S-CO2　recompression　cycle　and　that　of　S-CO2/T-CO2　combined　cycle　alter　consistently　with　the　changed　crucial　parameters　of　the　top　cycle.　©　2020,　Science　Press.　All　right　reserved.