Abstract: The investigation on the thermal-hydraulic behavior in SCWR fuel bundles is a very significant content of SCWR research. However, there is still a lack of understanding to predict the flow heat transfer behavior of supercritical fluid. In this paper, the heat transfer behavior of supercritical fluid in 4-rod bundle with spacer was numerically simulated. The effect of grid structure on the flow and heat transfer was discussed particularly. The numerical simulation using the SSG turbulent model gives a reasonable prediction compared with the experimental results. The calculation results show that the spacer significantly changes the velocity profile in the downstream, and enhances turbulent mixing and heat transfer. Consequently, the rod wall temperature appears more uniform in the circumferential direction and the peak wall temperature spot also shifts.