Abstract: The coupled radiation and convection heat transfer of a high temperature participating medium in a tube is investigated by numerical simulation.The medium with constant properties is gray and flows in a developing laminar status.The conservation equations governing the convection heat transfer are discretized by the control volume method (CVM) and solved by the SIMPLEC algorithm.The radiation transfer in medium is solved by the discrete ordinate method (DOM) and its contribution to the coupled heat transfer is dealt with as the source term in the energy equation.With different optical thickness of the medium and different tube wall temperatures,the numerical results of the temperature distribution in medium,the local radiation and convection heat fluxes at wall as well as the corresponding local Nusselt numbers are presented and discussed.The reliability of the numerical results is validated by comparing with the previous investigation and by analyzing the influence of discrete grid number.The results and analysis show that the thermal radiation of high temperature medium plays an important role in the coupled heat transfer of a developing laminar flow in the tube.It has a significant effect on the temperature distribution and influences the convection heat transfer.In addition,the tube wall temperature also influences the actions of radiation and convection in the coupled heat transfer.