Combined laminar forced convection and radiation heat transfer was numerically simulated in a three-dimensional channel flow. A finite volume method was used to solve the steady incompressible Navier-Stokes equations, energy equation, and radiative transfer equation. The effects of Reynolds number, conduction-radiation parameters, absorption coefficient, and scattering albedo on the Nusselt number and bulk temperature profiles along the channel are presented. Radiation was found to play a major impact on temperature field in the range of parameters considered in this study. It was found that the radiation effect is diminished, and thermal penetration is increased with increasing Reynolds number, conduction-radiation parameter, scattering albedo, and decreasing absorption coefficient.