Supercritical　heat　transfer　mechanisms　and　heat　transfer　correlations　are　firstly　reviewed　in　present　paper.　The　heat　transfer　characteristics　of　S-CO2　in　circumferentially　non-uniform　heated　vertical　upward　flow　are　then　numerically　studied　and　the　fundamental　mechanisms　are　discussed.　The　abnormal　heat　transfer　for　S-CO2　is　believed　to　be　caused　by　the　comprehensive　effect　of　thermophysical　property　variations.　For　S-CO2　with　non-uniform　heating　and　large　mass　flow　rate,　the　enhanced　heat　transfer　is　mainly　related　to　the　large　specific　heat　in　the　near　wall　region　while　the　deteriorated　heat　transfer　is　dominated　by　the　thickening　viscous　sublayer　induced　by　the　viscosity　increase.　Besides,　the　buoyancy　effect　induced　by　the　density　variation　is　still　prominent　to　axial　velocity　distribution　even　in　the　forced　convection.　Finally　a　new　correlation　with　higher　accuracy　is　developed　for　S-CO2　circumferentially　average　heat　transfer　by　introducing　the　correction　parameters　of　viscosity,　specific　heat,　axial　flow　acceleration　and　non-uniform　heat　flux.　(C)　2018　Elsevier　Ltd.　All　rights　reserved.