Abstract: In the heated upward mixed convection, the distributions of velocity and shear-stress vary significantly due to the existing of buoyancy force, leading to the laminarization of boundary layer and the delay of the onset of fully developed turbulent convection, and the heat transfer coefficient experiences a process from the deterioration, recovery and enhancement. The present investigation deals with the experiments in tubes of different diameters for the forced convection of pure steam and the forced convection and natural circulation of supercritical water. The research indicates that as the buoyancy force increases, the heat transfer deteriorates and reaches a minimum at a certain value of buoyancy force, then it turns to recovery and enhancement finally. The present investigation presents a correlation of heat transfer coefficients based on the experimental data for heated upward flow.