Heat transfer to supercritical water were investigated both experimentally and numerically. A 2-m long vertical upward smooth tube with a diameter of 19 mm was tested at pressures ranged from 11 to 32 MPa, values of mass flux from 170 to 800 kg.m(-2).s(-1) and heat fluxes up to 600 kW.m(-2). Various dimensionless parameters representing effects of property variations, buoyancy and thermal induced acceleration were estimated. Some of them show unique and strong relations to heat transfer coefficient, while no single behavior of independence is obtained with the majority of them. This result indicates additional parameters are required in case these dimensionless parameters are applied to predict supercritical heat transfer. Based on the experimental data, six typical correlations were evaluated. It turns out that the Mokry et al. correlation and Bishop et al. correlation show the best performance in predicting heat transfer. The shear stress transport kappa-omega model was employed to numerical analysis. Results of numerical prediction show a good agreement with experimental data, which proves the suitability of the present model. According to the result, physical mechanisms of both enhanced and deteriorated heat transfer at supercritical pressure are revealed. The integral effect of specific heat and buoyancy effect are the main reasons resulting in the abnormal heat transfer. (C) 2016 Elsevier Ltd. All rights reserved.