The thermal radiation has an effect on their thermal insulation performance when using silica aerogel composites at a high temperature. The effect of thermal radiation on the thermal conductivity of aerogel composites was investigated at different pressures and temperatures to regulate the gas phase heat transfer factors. The results show that the thermal conductivity of aerogel composites is decreased by 34% when the pressure is decreased from 100 kPa to 100 Pa under a weak radiant effect of 100℃, while the thermal conductivity is decreased by only 3% at 900℃ due to the thermal radiation effect. The effect of thermal radiation on the back surface temperature of aerogel composites was also investigated by a heat transfer model at different back surface temperatures. It is indicated that when the radiation heat transfer condition increases from 37 ℃ to 535℃, the temperature increase of the back of material model increases from 0 ℃ to 178 ℃ after removing the radiation heat transfer load between the back of the material model and environment. The temperature increase of the back of material model increases from 10 ℃ to 65 ℃ after removing the convection heat transfer load.