Abstract: In order to improve the turbulent heat transfer of supercritical carbon dioxide (S-CO₂) flowing in the horizontal tube, the simple and practical uniform sand-grain roughness is introduced into the pipe wall. Based on the heat transfer characteristics of horizontal supercritical fluids, an innovative roughening scheme targeting at the specific heat transfer degradation area near the top wall is proposed. During the simulations, k-ω SST turbulence model is employed and its predictions on the heat transfer of the rough piping flows have been validated against the experiments. Then, using the reliable simulation tool, the turbulent heat transfer of S-CO₂ within the 4.57mm-diameter horizontal tube is investigated, and the influences of regional roughness range and buoyancy strength are discussed. The results show that the regional roughness focusing on the top wall is able to significantly reduce the wall temperatures, enhance S-CO₂ heat transfer performances, and effectively improve the circumferential heat transfer uniformity. The effect of roughness areas is obvious within the upstream of the heated piping flow where the turbulent kinetic energy level is relatively low under the studied low-heat-flux condition. With the increase in heat flux, the buoyancy effect intensifies, and the high-temperature area near the top wall gradually expands. Under different operating conditions, the partially-roughen approach concentrating the high-temperature area of deterioration can obtain good performances, accounting both the heat transfer and extra flow resistance, can be achieved.