Abstract: The primary numerical simulation was presented on heat transfer behavior of supercritical water in smooth square annular channel. The simulation results indicate that the heat transfer behavior of supercritical water in smooth square channel is greatly non-uniformity in circumference. The heat transfer of the corner channel is better than that of the narrow channel. The heated wall temperature of the corner channel is lower than the heated wall temperature of the narrow channel at the same cross section. However, this circumferential non-uniformity increases along the axial distance, which increases most rapidly near the pseudo-critical point. It could be concluded that the main reason for the non-uniformity of heat transfer in circumference is the channel shape. It is important to pay more attention to the narrow channel of the SCWR when designing the core.