Abstract: An experimental investigation of turbulent heat transfer in vertical upward and downward supercritical carbon dioxide flow was conducted in a heated bare tube with an inner diameter of 10 mm.In the experimental conditions,it shows that the phenomenon of buoyancy and acceleration is obvious.For the upward cases,as the buoyancy effect increasing the forced convective heat transfer of carbon dioxide will transient to mixed convective heat transfer,then free convective heat transfer,in which the heat transfer capacity is weakened firstly,then resumed and strengthened.The acceleration often weakens the heat transfer capacity both for upward flow and downward flow.A new heat transfer correlation for vertical upward flow of supercritical carbon dioxide was developed,by which 95.03% of the predicted Nusselt numbers agree with the experimental data within ±30%.