Abstract: Numerical simulations of heat transfer to supercritical water in smooth square annular channel have been performed using fluid-solid coupling method.The simulation results indicated that the heat wall temperatures are non-uniformity on the circumference,and the temperature of inside heat wall is more uniform than the outside wall.It has been found that the average temperature of outside wall can be derived from the average temperature of inside wall using the one dimension differential equation.The temperature of the narrow channel reach the pseudo-critical point before the corner channel,which induce the circumferential non-uniformity of temperature on the outside wall varies along the axial distance and exhibits three regions with different patterns.Compared with the heat volume boundary condition,the heat flux boundary condition predict higher non-uniformity of wall temperature,which indicate the heat conduction in the solid domain smoothes the circumference temperature curve of the heat wall.