The inner flow and outer flow thermal environment has usually taken place in the inner surface of engine combustor and the outer surface of hypersonic vehicle, respectively. The two kinds of thermal environment have been compared by using the supersonic rectangle turbulent flow duct and arc heater. The cold-wall heat flux was measured and the engine combustor inner surface material was tested in two kinds of thermal environment. Due to the effect of thermal radiation heat transfer, the cold-wall heat flux of inner flow is respectively 21% and 40% higher than that of outer flow in two kinds of representative flow conditions. And the increments of the cold-wall heat fluxes are nearly equal, about 0.70~0.80MW/m2. So when the cold-wall heat flux increases, the effect of radiation heat transfer will gradually decrease. In material test experiment, the surface and rear temperature of the C/SiC composites in the inner flow is respectively higher about 400℃ and 90℃ than those with same formulation design in the outer flow, which is very significant to test the engine combustor inner surface material and must be considered in the material test experiment.