Abstract: 3D numerical simulation were performed on forced convection heat transfer in narrow rectangular channel with large aspect ratio under uniformly heating fluxes on the wide surfaces,while the narrow surfaces were kept under adiabatic condition.The simulation results agreed well with the experimental data.By using the 3D numerical simulation,effects of aspect ratio on temperature distribution of fluid in narrow rectangular channels were studied,and the results showed that for the narrow rectangular channels with large aspect ratio,heat concentration phenomena existed both in the corner regions and the center regions on the heating surfaces;The heat concentration at the center region of heating surfaces is weaker than that near the corner regions and will vanish with the decrease of the aspect ratio of the rectangular channel.In addition,due to false diffusion,low order interpolation scheme such as power scheme failed to predict the heat concentration at the center region of the heating surfaces.