Abstract: An experiment on the heat transfer of supercritical water in a 2×2 rod bundles with two paths was carried out. The two paths were separated by a square metal frame, where water flowed downward in the first path and turned to flow upward in the second path. The 2×2 heat rod bundles were installed in the second path, and cooled by the fluid flowing upward in the second path. The non-uniformity of circumferential wall temperature distribution in heat rod was observed. The effects of system parameters including mass flux, heat flux and pressure on the heat transfer were presented. The result shows that the heat transfer characteristics were similar to those observed in bare tube or annular tube.