Abstract: The experiment results of convection heat transfer of CO₂ at supercritical pressures in a 2 mm diameter vertical circular tube for upward flow and downward flow were analyzed for pressures ranging from 78 to 95 bar,inlet temperatures from to 25 to 40℃,and inlet Re numbers from 3000 to 20000.The results were compared with some well known empirical correlations for the heat transfer without buoyancy effects and the heat transfer with strong buoyancy effects.It is found that there is a big deviation between the ex-periment results and empirical correlations.Based on the experiment data,correlations are developed for the local Nusselt correlations of CO₂ at supercritical pressures in vertical circular tubes.