Abstract: A physical model was built to numerically investigate the nonuniform heat transfer characteristics of supercritical water within a triangle sub-channel. The corresponding fuel rod diameter was 8 mm and the pitch-to-diameter ratio was 1.4, respectively. Experimental result shows that the axial heat transfer is uneven and the axial heat transfer intensity has a peak value. The heat transfer coefficient is big when the supercritical water is in the pseudo-critical region and is small when the water is far away from the pseudo-critical region. The comparison between the experimental data and numerical result show that the SSG turbulence model can well predict the heat transfer characteristics of supercritical water in a triangle sub-channel of SCWR. The nonuniform heat transfer of supercritical water is seriously in the sub-channel. In the mainstream direction, the heat transfer from the inner wall to the fluid is enhanced in the great specific heat region and weakened in the high enthalpy region. The local heat transfer coefficient increases first and then decreases with the increasing of the circumferential angle, which reaches a peak in the central region and a trough near the narrow gap. The degree of circumferential heat transfer nonuniformity also differs in different enthalpy regions. Moreover, with the increasing of the pitch-to-diameter ratio, the average wall temperature rises and the heat transfer coefficient decreases, and the circumferential heat transfer nonuniformity reduces significantly.