The　comprehensive　understanding　of　heat　transfer　characteristics　to　supercritical　carbon　dioxide　in　flowing　channels　is　significant　for　the　design　and　safe　operation　in　the　advanced　supercritical　carbon　dioxide　systems,　especially　for　the　heat　transfer　deterioration　conditions　that　is　generally　occurs　at　relatively　low　mass　fluxes　but　high　heat　fluxes.　This　paper　experimentally　studied　the　heat　transfer　behaviors　of　supercritical　carbon　dioxide　flowing　in　a　vertical　heated　mini-tube　with　an　inner　diameter　of　2　mm.　The　experiment　was　conducted　with　pressure　of　7.5–9　MPa,　low　(G　−2·s−1)/high　mass　flux　of　(G　＞　200　kg·m−2·s−1)　and　heat　flux　of　45–300　kW·m−2.　The　effects　of　operational　parameters,　buoyancy　force　and　flow　acceleration　on　convective　heat　transfer　were　discussed.　The　results　showed　that　at　low　mass　fluxes,　no　obvious　heat　transfer　deterioration　behaviors　observed　even　though　heat　load　(q/G)　was　high.　However,　under　the　similar　q/G　conditions　with　high　mass　fluxes,　a　remarkable　heat　transfer　deterioration　occurs.　Under　low　mass　fluxes,　heat　transfer　enhanced　by　the　strong　buoyancy　force　and　obvious　acceleration　effect,　but　at　high　mass　fluxes,　deteriorated　heat　transfer　mainly　effected　by　buoyancy　rather　than　acceleration　effect.　Based　on　the　experimental　data　and　multiple　effects　of　buoyancy　and　thermal　acceleration,　an　improved　correlation　considering　these　effects　at　low　mass　fluxes　was　proposed,　where　more　than　90%　data　in　the　within　±　20%　error　range.　©　2021